Lens barrel and a zoom lens barrel

ABSTRACT

A lens barrel includes first and second lens groups guided in an optical axis direction without rotating about the optical axis, first and second support frames which support the first and second lens groups and include first and second cam followers, respectively; and a cam ring which is rotatable about the optical axis and includes a cam groove. The cam groove is formed as a continuous groove and includes first and second groove portions via which the first and second cam followers are guided to move the first and second lens groups, respectively. One of the first cam follower and the second cam follower enters one of the first groove portion and the second groove portion after passing through the other of the first groove portion and the second groove portion in a preparation stage of the lens barrel.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a lens barrel, and also relatesto a zoom lens barrel.

[0003] 2. Description of the Related Art

[0004] As an example of a conventional lens barrel in which two or morelens groups move in an optical axis direction, a lens barrel in whichfront and rear lens groups are guided linearly in the optical axisdirection without rotating about the optical axis and in which the lenssupport frame of each of the front and rear lens groups is provided witha set of follower pins which are respectively engaged in a correspondingset of cam grooves (cam slots) formed on a cam ring is known in the art.In this type of lens barrel, one cam groove is necessary for eachfollower pin formed on the lens support frame of each of the front andrear lens groups.

[0005] Accordingly, a large number of cam grooves are necessary if thelens barrel is provided with a plurality of movable lens groups. It isdifficult to form a large number of cam grooves on a cam ring due to alimited circumferential area thereon. This is more serious if thediameter of the cam ring is small.

[0006] One possible solution would be to increase the pitch of each camgroove (i.e., to increase the angle of inclination of each cam grooverelative to a circumferential direction of the cam ring), however, thisimpairs the movement of the follower pins, or may lock the followerpins. If the number of the follower pins is large, the number of the camgrooves formed on the cam ring is also large, which inevitablydeteriorates the strength of the cam ring.

[0007] As an example of a conventional extendable lens barrel such as anextendable zoom lens barrel in which two or more lens groups move in anoptical axis direction, an extendable lens barrel in which front andrear lens groups are guided linearly in the optical axis directionwithout rotating about the optical axis, and in which the lens supportframe of each of the front and rear lens groups is provided with a setof follower pins which are respectively engaged in a corresponding setof cam grooves (cam slots) formed on a cam ring, is known in the art.Note that the term ‘extendable lens barrel’ refers to a lens barrelwhich extends and retracts so that the length thereof is shortest at anaccommodation position, and is longer at a photographing position.

[0008] In such an extendable lens barrel, if the lens barrel isretracted to move each of the front and rear lens groups to anaccommodation position thereof, each follower pin of the lens supportframe of each lens group is accommodated and positioned at an end(accommodation position) of the associated cam groove with no gapbetween the follower pin and the end of the cam groove, and accordingly,each follower pin cannot move from the accommodation position thereofunless the extendable lens barrel is extended to move each of the frontand rear lens groups out of the accommodation position thereof.

[0009] However, if the respective accommodation positions of the frontand rear lens groups are precisely determined by the profiles of the camgrooves, the front and rear lens groups at their respectiveaccommodation positions need to have a certain gap therebetween so asnot to collide with each other, which makes it difficult to reduce thelength of the extendable lens barrel in an accommodation state thereof.

[0010] In addition, since it is necessary to adjust the fixing positionof at least one lens group relative to a support frame thereof in theoptical axis direction when the lens group is fixed to the lens supportframe during assembly, a marginal space for the fixing positionadjustment needs to be secured between the respective accommodationpositions of adjacent lens groups, which makes it more difficult toreduce the length of the extendable lens barrel in an accommodationstate thereof.

[0011] In an extendable lens barrel which extends and retracts betweenan extended position (ready-to-photograph position) and an accommodationposition, if it is desired to reduce the length of the extendable lensbarrel in an accommodation state thereof, all of the movable lens groupspositioned in the lens barrel need to be retracted in order to be ascompact as possible in an accommodation position of the extendable lensbarrel.

[0012] However, in the case where the extendable lens barrel is providedat the front end thereof with a photographing aperture and at least onelens barrier blade which opens and closes the photographing aperture ina plane perpendicular to the optical axis of the extendable lens barrel,a substantial gap has to be provided between the front surface of thefront-end lens group and the lens barrier blade, which increases thelength of the extendable lens barrel.

SUMMARY OF THE INVENTION

[0013] The present invention provides a lens barrel wherein a cam ringdoes not need to have a large diameter even if the lens barrel isprovided with a large number of movable lens groups, and wherein the camring can be provided with cam grooves which ensure smooth movements ofthe associated follower pins while keeping any decrease in strength ofthe cam ring to a minimum.

[0014] The present invention also provides a lens barrel wherein each ofa plurality of lens groups provided in the lens barrel can beaccommodated (housed) as compact as possible while preventing adjacentlens groups from contacting with each other even if the lens barrel isof a type wherein at least one lens group is fixed to the lens supportframe thereof while the fixing position of the lens group is beingadjusted relative to the lens support frame thereof in the optical axisdirection, or even if the lens barrel is an extendable lens barrelprovided at the front end thereof with a photographing aperture and atleast one lens barrier blade which opens and closes the photographingaperture.

[0015] The present invention also provides a extendable zoom lens barrelhaving two or more movable lens groups, wherein front and rear lensgroups can be accommodated compact in size in the zoom lens barrel whenit is in an accommodation state.

[0016] For example, in an embodiment, a lens barrel is provided,including first and second lens groups guided in an optical axisdirection without rotating about the optical axis; a first support framewhich supports the first lens group, the first support frame including afirst cam follower; a second support frame which supports the secondlens group, the second support frame including a second cam follower;and a cam ring which is driven to rotate about the optical axis, the camring including a cam groove in which the first cam follower and thesecond cam follower are engaged. The cam groove is formed as acontinuous groove and includes a first groove portion via which thefirst cam follower is guided to move the first lens group, and a secondgroove portion via which the second cam follower is guided to move thesecond lens group. The cam groove is formed so that one of the first camfollower and the second cam follower enters a corresponding one of thefirst groove portion and the second groove portion after passing throughthe other of the first groove portion and the second groove portion in apreparation stage of the lens barrel.

[0017] The first groove portion can include a first zooming section formoving the first lens group to perform a zooming operation; and a firstaccommodation section in which the first cam follower is positioned whenthe first lens group is accommodated. The second groove portion caninclude a second zooming section for moving the second lens group toperform the zooming operation; and a second accommodation section inwhich the second cam follower is positioned when the first lens group isaccommodated. The first zooming section, the second zooming section, thefirst accommodation section and the second accommodation section arearranged in that order from one end of the cam groove, so that the firstcam follower passes through the second zooming section when movingbetween the first accommodation section and the first zooming section.

[0018] It is desirable for the first lens group to be positioned infront of the second lens group.

[0019] Each of the first lens group and the second lens group canconstitute a lens element of a zoom lens optical system, the cam ringbeing driven to move the first lens group and the second lens group inthe optical axis direction while changing a distance therebetween tovary a focal length.

[0020] The lens barrel can further include a third lens group positionedbehind the second lens group and guided in the optical axis direction,wherein the third lens group constitutes a focusing lens and is moved inthe optical axis direction to perform a focusing operation.

[0021] In another embodiment, a lens barrel includes a front lenssupport member which supports a front lens group and is guided in anoptical axis direction without rotating about the optical axis; a rearlens support member which supports a rear lens group and is guided inthe optical axis direction without rotating about the optical axis; anda support frame movement mechanism for moving the front lens supportmember and the rear lens support member between respectiveready-to-photograph positions and respective accommodation positionslocated behind the respective ready-to-photograph positions, in theoptical axis direction. The support frame movement mechanism brings thefront lens support member and the rear lens support member into contactwith each other at the respective accommodation positions withoutcausing the front lens group and the second lens group to come intocontact with each other.

[0022] The support frame movement mechanism can include a biasingdevice; the support frame movement mechanism can bring the front lenssupport member and the rear lens support member into contact with eachother, with a biasing force of the biasing device, at the respectiveaccommodation positions.

[0023] The support frame movement mechanism can include a first camfollower formed on the front lens support member; a second cam followerformed on the rear lens support member; and a cam ring which is drivento rotate about the optical axis, the cam ring including a cam groove inwhich the first cam follower and the second cam follower are engaged.The cam groove can include a front lens group moving section for movingthe front lens support member to the ready-to-photograph position; arear lens group moving section for moving the rear lens support memberto the ready-to-photograph position; a front lens group accommodationsection for allowing the front lens group to move to the accommodationposition which is located behind a position of the front lens group inthe optical axis direction when the first cam follower is positioned inthe front lens group moving section; and a rear lens group accommodationsection for allowing the rear lens group to move to the accommodationposition which is located behind a position of the rear lens group inthe optical axis direction when the second cam follower is positioned inthe rear lens group moving section. The front lens group accommodationsection defines a clearance between the front lens group accommodationsection and the first cam follower so that the first cam follower ismovable in the optical axis direction in the front lens groupaccommodation section. The rear lens group accommodation section definesa clearance between the rear lens group accommodation section and thesecond cam follower so that the second cam follower is movable in theoptical axis direction in the rear lens group accommodation section.

[0024] The front lens group moving section and the rear lens groupmoving section constitute a first zooming section and a second zoomingsection, respectively, for varying a focal length to perform a zoomingoperation.

[0025] The biasing device can bias the front lens support member in adirection toward the accommodation position so that the front lenssupport member moves to come in contact with the rear lens supportmember.

[0026] It is desirable for an area of the front lens group accommodationsection to be smaller than an area of the rear lens group accommodationsection.

[0027] In another embodiment, lens barrel having an optical systemincluding of a plurality of lens groups, the lens barrel including alens supporting frame to which a frontmost lens group of the pluralityof lens groups is supported; a first moving frame to which the lenssupporting frame is supported via male and female screw-threadedportions meshing with each other, one and the other of the male andfemale screw-threaded portions being formed on the lens supporting frameand the first moving frame, respectively; a second moving frame to whicha rear lens group of the plurality of lens groups which is positionedbehind the frontmost lens group is supported; and a support framemovement mechanism for moving the first moving frame and the secondmoving frame between respective ready-to-photograph positions andrespective accommodation positions located behind the respectiveready-to-photograph positions in a direction of an optical axis. Asupporting position of the lens supporting frame, relative to the firstmoving frame in the optical axis direction, can be adjusted via the maleand female screw-threaded portions during assembly. The support framemovement mechanism brings the lens supporting frame and the secondmoving frame into contact with each other when positioning the firstmoving frame and the second moving frame at the respective accommodationpositions without causing the frontmost lens group and the rear lensgroup to come into contact with each other regardless of the adjustmentof the supporting position of the lens supporting frame.

[0028] The support frame movement mechanism can include a biasingdevice; and the support frame movement mechanism can bring the lenssupporting frame and the second moving frame into contact with eachother, with a biasing force of the biasing device, when the first movingframe and the second moving frame are positioned at the respectiveaccommodation positions.

[0029] The support frame movement mechanism can include a first camfollower formed on the first moving frame; a second cam follower formedon the second moving frame; and a cam ring which is driven to rotateabout the optical axis, the cam ring including a cam groove in which thefirst cam follower and the second cam follower are engaged. The camgroove can include a frontmost lens group moving section for moving thefirst moving frame to the ready-to-photograph position; a rear lensgroup moving section for moving the second lens frame to theready-to-photograph position; a frontmost lens group accommodationsection for allowing the frontmost lens group to move to theaccommodation position which is located behind a position of thefrontmost lens group in the optical axis direction when the first camfollower is positioned in the frontmost lens group moving section; and arear lens group accommodation section for allowing the rear lens groupto move to the accommodation position which is located behind a positionof the rear lens group in the optical axis direction when the second camfollower is positioned in the rear lens group moving section. Thefrontmost lens group accommodation section defines a clearance betweenthe frontmost lens group accommodation section and the first camfollower so that the first cam follower is movable in the optical axisdirection in the frontmost lens group accommodation section, whereby thefrontmost lens group and the rear lens group are not in contact witheach other in a state where the lens supporting frame and the secondmoving frame are in contact with each other when the first moving frameand the second moving frame are located at the respective accommodationpositions. The clearance includes at least a predetermined widthcorresponding to a maximum variation amount by the adjustment of thesupporting position of the lens supporting frame.

[0030] The support frame movement mechanism can include a first camfollower formed on the first moving frame; a second cam follower formedon the second moving frame; and a cam ring which is driven to rotateabout the optical axis, the cam ring including a cam groove in which thefirst cam follower and the second cam follower are engaged. A width ofthe cam groove in the optical axis direction at a position correspondingto the accommodation position, when the first moving frame is positionedat the accommodation position, is formed so that a clearance between thecam groove and the first cam follower is greater than an adjustmentrange of a position of the lens supporting frame relative to the firstmoving frame in the optical axis direction.

[0031] The biasing device can include at least one helical compressionspring.

[0032] In another embodiment, a lens barrel can include at least onelens group which moves in an optical axis direction; a ring member whichis provided around the lens group, the ring member having aphotographing aperture at a front end of the ring member; and at leastone barrier blade positioned at the front end of the ring member, thebarrier blade being driven to open and close the photographing aperture.A frontmost surface of the lens group can be formed as a convex surface.The barrier blade can include a concave surface which is formed on arear surface thereof so that a shape of the concave surface correspondsto a shape of a corresponding portion of the frontmost surface. Thebarrier blade can be driven to open and close the photographing aperturein a plane perpendicular to the optical axis at a position wherecollision between the barrier blade and the convex front surface of thelens group is avoided due to the presence of the concave surface.

[0033] It is desirable for the lens group to include a front lens groupand a rear lens group, the extendable lens barrel further including afront lens support member which supports the front lens group and isguided in the optical axis direction without rotating about the opticalaxis; a rear lens support member which supports the rear lens group andis guided in the optical axis direction without rotating about theoptical axis; and a support frame movement mechanism for moving thefront lens support member and the rear lens support member betweenrespective ready-to-photograph positions and respective accommodationpositions located behind the respective ready-to-photograph positions inthe optical axis direction, respectively. The support frame movementmechanism can bring the front lens support member and the rear lenssupport member into contact with each other at the respectiveaccommodation positions without causing the front lens group and thesecond lens group to come into contact with each other.

[0034] The support frame movement mechanism can include a biasingdevice, and the support frame movement mechanism can bring the frontlens support member and the rear lens support member into contact witheach other, with a biasing force of the biasing device, at therespective accommodation positions.

[0035] It is desirable for the front lens group to include a frontmostlens group of the lens group. The front lens support member includes alens supporting frame to which the frontmost lens group is supported,and a first moving frame to which the lens supporting frame is supportedvia male and female screw-threaded portions meshing with each other, oneand the other of the male and female screw-threaded portions beingformed on the lens supporting frame and the first moving frame,respectively. A supporting position of the lens supporting frame,relative to the first moving frame in the optical axis direction, can beadjusted via the male and female screw-threaded portions duringassembly. The support frame movement mechanism can bring the lenssupporting frame and the rear lens support member into contact with eachother when positioning the front lens support member and the rear lenssupport member at the respective accommodation positions without causingthe frontmost lens group and the rear lens group to come into contactwith each other regardless of the adjustment of the supporting positionof the lens supporting frame.

[0036] The lens group can constitute a lens element of a zoom lensoptical system for varying a focal length.

[0037] The barrier blade can include a pair of barrier blades; and theconcave surface can include a pair of semi-circular concave faces whichare formed on the pair of barrier blades, respectively, the pair ofsemicircular concave faces together forming a circular concave face, thecircular concave face corresponding to the shape of a central portion ofthe convex frontmost surface in a state where the pair of barrier bladesare closed.

[0038] In another embodiment, a lens barrel is provided, including frontand rear lens groups guided in a direction of an optical axis withoutrotating about the optical axis; a first support frame which supportsthe front lens group, the first support frame including a first camfollower; a second support frame which supports the rear lens group, thesecond support frame including a second cam follower; and a cam ringwhich is driven to rotate about the optical axis, the cam ring includinga first groove portion and a second groove portion in which the firstcam follower and the second cam follower are engaged, respectively. Thefirst groove portion includes a first operating section for moving thefront lens group to a position wherein a photographing operation isperformed; and a first accommodation section for moving the front lensgroup to a first accommodation position which is located behind aposition of the front lens group in the optical axis direction when thefirst cam follower is positioned in the first operating section. Thesecond groove portion includes a second operating section for moving therear lens group to perform the zooming operation; and a secondaccommodation section for photographing the rear lens group to a secondaccommodation position which is located behind a position of the rearlens group in the optical axis direction when the second cam follower ispositioned in the second photographing section. At least one of thefirst accommodation section and the second accommodation section isformed to allow corresponding at least one of the first cam follower andthe second cam follower to move in the optical axis direction incorresponding the at least one of the first accommodation section andthe second accommodation section.

[0039] The first accommodation section and the second accommodationsection can be formed so that the front lens group and the rear lensgroup are released from constraints of the first accommodation sectionand the second accommodation section at the first accommodation positionand the second accommodation position, respectively.

[0040] The cam groove can be formed as a continuous groove including thefirst groove portion and the second groove portion.

[0041] It is desirable for the first groove portion, the second grooveportion, the first accommodation section and the second accommodationsection to be arranged in that order from one end of the cam groove, sothat the first cam follower passes through the second groove portionwhen moving between the first accommodation section and the first grooveportion.

[0042] The second operating section of the second cam groove can beformed adjacent to the first operating section of the first cam grooveportion, and the first accommodation section of the first cam grooveportion can be formed adjacent to the second operating section, and thesecond accommodation section of the second cam groove can be formedadjacent to the first accommodation section.

[0043] In another embodiment, a lens barrel is provided, including aplurality of lens groups guided in an optical axis direction withoutrotating about the optical axis; a plurality of support frames whichsupport the plurality of lens groups, respectively; a plurality of camfollowers formed on the plurality of support frames, respectively; and acam ring which is driven to rotate about the optical axis, the cam ringincluding a plurality of cam grooves in which the plurality of camfollowers are engaged, respectively. Each of the plurality of camgrooves includes an operating section for moving corresponding one ofthe plurality of lens groups to perform a photographing operation; andan accommodation section for moving the corresponding one lens group toan accommodation position which is located behind a position of thecorresponding one lens group in the optical axis direction whencorresponding one of the plurality of cam followers is engaged in theoperating section. The accommodation section is formed to allow thecorresponding one cam follower to move in the optical axis direction inthe accommodation section.

[0044] The present disclosure relates to subject matter contained inJapanese PatentApplications Nos.2001-83262, 2001-83263, 2001-83683,2001-83684 and 2001-83691 (all filed on Mar. 22, 2001) which areexpressly incorporated herein by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The present invention will be described below in detail withreference to the accompanying drawings in which:

[0046]FIG. 1 is an exploded perspective view of an embodiment of a zoomlens barrel according to the present invention;

[0047]FIG. 2 is an exploded perspective view of an upper left portion ofthe zoom lens barrel shown in FIG. 1;

[0048]FIG. 3 is an exploded perspective view of a middle portion of thezoom lens barrel shown in FIG. 1;

[0049]FIG. 4 is an exploded perspective view of a lower right portion ofthe zoom lens barrel in FIG. 1;

[0050]FIG. 5 is an axial cross sectional view of the zoom lens barrelshown in FIG. 1, above the optical axis, showing the zoom lens barrel inan accommodation state;

[0051]FIG. 6 is an axial cross sectional view of the zoom lens barrelshown in FIG. 1, above the optical axis, taken along a plane differentfrom that of FIG. 5, showing the zoom lens barrel in an accommodationstate;

[0052]FIG. 7 is an axial cross sectional view of the zoom lens barrelshown in FIG. 1, showing the zoom lens barrel in an accommodation stateabove the optical axis, and further showing the zoom lens barrel in aready-to-photograph state below the optical axis;

[0053]FIG. 8 is a developed view of an outer peripheral surface of a camring provided as an element of the zoom lens barrel shown in FIG. 1;

[0054]FIG. 9 is a developed view of one of three cam grooves formed onan inner peripheral surface of the cam ring, showing the profile of thecam groove;

[0055]FIG. 10 is a developed view of two of the three cam grooves shownin FIGS. 8 and 9, showing the relationship between the cam grooves,first follower pins formed on a first lens frame, and second followerpins formed on a second lens frame;

[0056]FIG. 11 is a schematic developed view of a cam-ring-control camslot formed on a stationary ring and an associated rotation transfergroove formed on a rotatable ring;

[0057]FIG. 12 is a front elevational view of the zoom lens barrel with abarrier blade support front plate removed therefrom in a state where apair of lens barrier blades are closed;

[0058]FIG. 13 is a view similar to that of FIG. 12 and illustrates thebarrier drive ring and peripheral elements thereof in a state where thepair of lens barrier blades are open;

[0059]FIG. 14 is a view similar to that of FIG. 12 and illustrates thepair of barrier blades of a barrier unit, showing the relationshipbetween the pair of barrier blades and an inner ring;

[0060]FIG. 15 is a graph showing variations of respective axialpositions of first and second lens groups (first and second lens frames)in a range of movement including a zooming section and a retractingsection;

[0061]FIG. 16 is a developed view of the cam ring and the barrier drivering, showing the positional relationship therebetween; and

[0062]FIG. 17 is an enlarged perspective view of a lens barrier bladeshown in FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0063] An embodiment of a zoom lens barrel, an exploded perspective viewof which is shown in FIG. 1, is a extendable zoom lens barrel of adigital camera.

[0064] The zoom lens barrel 1 is provided with a support frame movementmechanism which is constructed from a set of three follower pins (firstcam followers) 18 f fixed to a first lens group moving frame (firstsupport frame) 18, a set of three follower pins (second cam followers)19 f fixed to a second lens group moving frame (second supportframe/rear lens support member) 19, a cam ring 15, a set of three linearguide holes 18 a of the first lens group moving frame 18, a set of threelinear guide bosses 17 d (only one of which appears in FIGS. 1 and 3) ofan inner ring (ring member) 17, a set of three linear guide grooves 18 cof the first lens group moving frame 18, and a set of three linear guidekeys 19 a of the second lens group moving frame 19.

[0065] As can be clearly seen in FIGS. 5 through 7, the zoom lens barrel1 is provided with a photographing optical system constructed from threelens groups: a first lens group L1, a second lens group L2, and a thirdlens group L3, in that order from the object side (the left side asviewed in each of FIGS. 5 through 7). The first and second lens groupsL1 and L2 are driven to move along an optical axis O relative to thethird lens group L3 while varying the distance therebetween to perform azooming operation. The third lens group L3 serves as a focusing lensgroup, and is driven to move along the optical axis O to perform afocusing operation.

[0066] The zoom lens barrel 1 is provided with a housing 11, a shaftholding member 12 and a stationary ring 13, which are all stationarymembers fixed to a camera body (not shown). Accordingly, the housing 11,the shaft holding member 12 and the stationary ring 13 do not move inthe direction of the optical axis O (i.e., in the optical axisdirection) or rotates about the optical axis O. The housing 11 isprovided at a rear end thereof with a flange 11 a (see FIG. 4), whilethe stationary ring 13 is provided at a rear end thereof with a flange13 a which is fixed to the flange 11 a of the housing 11. The housing 11is provided with an outer cylindrical portion 11 b and a filter holdingportion 11 c to which a low-pass filter 11 d is fixed. As shown in FIGS.5 through 7, the low-pass filter 11 d is positioned in front of a CCD(solid-state image pick-up device) 10 a fixed to a stationary base 10positioned in the camera body.

[0067] The stationary ring 13 is positioned inside the outer cylindricalportion 11 b of the housing 11. The zoom lens barrel 1 is provided, onthe stationary ring 13 between the stationary ring 13 and the outercylindrical portion 11 b, with a rotatable ring 14. The stationary ring13 is positioned inside the rotatable ring 14 which supports the camring 15 therein. The stationary ring 13 is provided with a set of threecam slots (cam-ring-control cam slots) 13 b formed on the stationaryring 13 as through-slots at equi-angular intervals in a circumferentialdirection thereof. The cam ring 15 is provided at the rear end thereofwith a thick-wall cylinder portion 15 a. A set of three follower pins 15b fixed to the thick-wall cylinder portion 15 a at equiangular intervalsin a circumferential direction of the cam ring 15 pass through the setof three cam slots 13 b of the stationary ring 13 to be engaged in a setof three rotation transfer grooves 14 a (only of which appears in FIGS.1 and 4) which are formed on an inner peripheral surface of therotatable ring 14.

[0068]FIG. 11 shows a developed view of one of the three cam slots 13 band the associated one of the three rotation transfer grooves 14 a. Eachrotation transfer groove 14 a includes a linear groove portion 14 a 1,an inclined groove portion 14 a 2, and a circumferential groove portion14 a 3 in that order from the front end to the rear end of the lineargroove portion 14 a 1 (from left to right as viewed in FIG. 11). Thelinear groove portion 14 a 1, which occupies a major portion of therotation transfer groove 14 a, extends parallel to the optical axis O.The circumferential groove portion 14 a 3 of each rotation transfergroove 14 a is used only when the zoom lens barrel 1 isassembled/disassembled. Each cam slot 13 b includes a linear slotportion 13 b 1, a state-changing slot portion 13 b 2, a zooming slotportion 13 b 3, and a terminal slot portion 13 b 4, in that order fromthe end (the lower end as viewed in FIG. 11) of the cam slot 13 b whichclosest to the rear end of the stationary ring 13. The linear slotportion 13 b 1 extends parallel to the optical axis O. Thestate-changing slot portion 13 b 2 extends in a direction inclined withrespect to both the optical axis o and a circumferential direction ofthe stationary ring 13. The zooming slot portion 13 b 3 extends in acircumferential direction of the stationary ring 13. The terminal slotportion 13 b 4 is used only when the zoom lens barrel 1 isassembled/disassembled.

[0069] The rotating barrel 14 rotates about the optical axis O in arotational range between an accommodation position (accommodationposition) and a telephoto extremity via a wide-angle extremity. Thisrotational range includes a preparation section (preparation stage)which extends between a position close to the accommodation position andthe wide-angle extremity, and a zooming section which extends betweenthe wide-angle extremity to the telephoto extremity (see FIG. 11). Ifthe rotatable ring 14 rotates relative to the stationary ring 13 in astate where each follower pin 15 b is engaged in the inclined grooveportion 14 a 2 of the associated rotation transfer groove 14 a and thelinear slot portion 13 b 1 of the associated cam slot 13 b (i.e., in astate where the rotatable ring 14 is in the accommodation position andwhere the cam ring 15 is fully retracted), each follower pin 15 b of thecam ring 15 is pressed by a side edge of the linear slot portion 13 b 1of the associated cam slot 13 b, which causes the cam ring 15 to move inthe optical axis direction along the linear slot portion 13 b 1 withoutrotating about the optical axis O. If the rotatable ring 14 rotatesrelative to the stationary ring 13 in a state where each follower pin 15b is engaged in the linear groove portion 14 a 1 of the associatedrotation transfer groove 14 a and the state-changing slot portion 13 b 2of the associated cam slot 13 b (i.e., in a state where the rotatablering 14 is in the preparation section), each follower pin 15 b of thecam ring 15 moves along the state-changing slot portion 13 b 2 of theassociated cam slot 13 b, which causes the cam ring 15 to rotate aboutthe optical axis O while moving in the optical axis direction due to theengagement of the follower pin 15 b with the state-changing slot portion13 b 2. If the rotatable ring 14 rotates relative to the stationary ring13 in a state where each follower pin 15 b is engaged in the lineargroove portion 14 a 1 of the associated rotation transfer groove 14 aand the zooming slot portion 13 b 3 of the associated cam slot 13 b(i.e., in a state where the rotatable ring 14 is in the zoomingsection), each follower pin 15 b of the cam ring 15 moves along thezooming slot portion 13 b 3 of the associated cam slot 13 b, whichcauses the cam ring 15 to rotate about the optical axis O without movingin the optical axis direction.

[0070] The rotatable ring 14 is provided on an outer peripheral surfacethereof with a circumferential gear 14 b which is in mesh with a drivepinion (not shown). The drive pinion is driven by a reversible motor(not shown) to rotate forwardly and reversely. Rotation of the drivepinion causes the rotatable ring 14 to rotate to thereby move the camring 15 in the optical axis direction while rotating about the opticalaxis O. Accordingly, if the accommodation position of the cam ring 15 isregarded as a starting position (reference position) of movement of thecam ring 15, firstly the cam ring 15 moves linearly in the optical axisdirection without rotating about the optical axis O (due to the linearslot portions 13 b 1), subsequently the cam ring 15 moves in the opticalaxis direction while rotating about the optical axis O (due to thestate-changing slot portions 13 b 2 in the preparation section), andfinally the cam ring 15 rotates about the optical axis O without movingin the optical axis direction (due to the zooming slot portion 13 b 3 inthe zooming section).

[0071] In the present embodiment of the zoom lens barrel 1, therotatable ring 14, the cam ring 15 and a barrier drive ring 31 arerotatable elements. The remaining movable elements, except for thesecond lens group moving frame 19, linearly move in the optical axisdirection without rotating about the optical axis O. The second lensgroup moving frame 19 can rotate about the optical axis O slightly. Suchlinearly moving elements and guiding mechanisms thereof will behereinafter discussed. The zoom lens barrel 1 is provided between thestationary ring 13 and the cam ring 15 with an outer ring 16 and theinner ring 17 which is provided inside the outer ring 16. The outer ring16 and the inner ring 17 are positioned in an annular space between thecam ring 15 and the stationary ring 13, while the thick-wall cylinderportion 15 a of the cam ring 15 is engaged with an inner peripheralsurface of the stationary ring 13 so that the cam ring 15 can rotateabout the optical axis O relative to the stationary ring 13 withouttilting relative to the optical axis O.

[0072] As shown in FIG. 2, the outer ring 16, which is positionedimmediately inside of the stationary ring 13, includes a main ring body16 r and a reinforcing ring 16 x which are made of synthetic resin andmetal, respectively. The main ring body 16 r is provided at a rear endthereof with a thick-wall cylinder portion 16 a, and is furtherprovided, on the thick-wall cylinder portion 16 a at equi-angularintervals in a circumferential direction of the main ring body 16 r,with a set of three linear guide keys 16 b (only one of which appears inFIGS. 1 and 2) which extend radially outwards. The stationary ring 13 isprovided on an inner peripheral surface thereof with a set of threelinear guide grooves 13 c which extend parallel to the optical axis O,and in which the set of three linear guide keys 16 b of the main ringbody 16 r are slidably engaged in the set of three linear guide keys 16b, respectively. The metal reinforcing ring 16 x is fitted on, andadhered to, an outer peripheral surface of the main ring body 16 r infront of the thick-wall cylinder portion 16 a by an adhesive toreinforce the main ring body 16 r with a minimum increase in wallthickness of the outer ring 16, which contributes to a reduction in wallthickness of the zoom lens barrel 1, i.e., contributes to furtherminiaturization of the zoom lens barrel 1.

[0073] Similar to the outer ring 16, the inner ring frame 17 includes amain ring body 17 r and a reinforcing ring 17 x which are made ofsynthetic resin and metal, respectively. The main ring body 17 r isprovided at a rear end thereof with a thick-wall cylinder portion 17 a.The metal reinforcing ring 17 x is fitted on and adhered to an outerperipheral surface of the main ring body 17 r in front of the thick-wallcylinder portion 17 a by an adhesive to reinforce the main ring body 17r with a minimum increase in wall thickness of the inner ring 17, whichcontributes to a reduction in wall thickness of the zoom lens barrel 1,i.e., contributes to further miniaturization of the zoom lens barrel 1.

[0074] The outer ring 16 is provided, on an inner peripheral surface ofthe main ring body 16 r at equi-angular intervals in a circumferentialdirection of the outer ring 16, with a set of three linear guide grooves16 c which extend parallel to the optical axis O. The inner ring 17 isprovided on the thick-wall cylinder portion 17 a with a set of threelinear guide keys 17 b which extend radially outwards to be slidablyengaged in the set of three linear guide grooves 16 c of the main ringbody 16 r, respectively. The outer ring 16 is provided at the rear endthereof with a set of three bayonet prongs 16 d (only one of whichappears in FIG. 5) which extend radially inwards. The cam ring 15 isprovided, in the vicinity of the rear end thereof immediately in frontof the thick-wall cylinder portion 15 a, with a circumferential groove15 c in which the set of three bayonet prongs 16 d are engaged to bemovable in the circumferential groove 15 c within a predetermined angleof rotation. When the cam ring 15 is positioned within an operatingangle relative to the outer ring 16, the cam ring 15 and the outer ring16 are movable together in the optical axis direction withoutdisengaging from each other, and at the same time, the cam ring 15 isrotatable about the optical axis O relative to the outer ring 16 due tothe engagement of the set of three bayonet prongs 16 d with thecircumferential groove 15 c.

[0075] The main ring body 17 r of the inner ring 17 is provided in thevicinity of the front end thereof with an inner flange 17 c whichextends radially inwards and to which a barrier unit 40 and the barrierdrive ring 31 are fixed. The main ring body 17 r of the inner ring 17 isprovided, on an rear face of the inner flange 17 c at equi-angularintervals in a circumferential direction of the inner ring 17, with theset of three linear guide bosses 17 d (only one of which appears inFIGS. 1 and 3). The zoom lens barrel 1 is provided with the first lensgroup moving frame 18 which is provided in the inner ring 17. The firstlens group moving frame 18 is provided at the front end thereof with aninner flange 18 b which extends radially inwards to form a circularaperture having the center thereof about the optical axis O. A femalethread portion 18 d is formed on an inner peripheral face of the innerflange 18 b. The first lens group moving frame 18 is provided on theinner flange 18 b with the set of three linear guide holes 18 a in whichthe set of three linear guide bosses 17 d of the inner ring 17 areslidably engaged, respectively. Each linear guide hole 18 a is formedhaving an oval cross section which is elongated in a radial direction ofthe first lens group moving frame 18. Even if each linear guide boss 17d is fitted in the associated linear guide hole 18 a with a substantialclearance therebetween, the inner ring 17 is guided in the optical axisdirection relative to the first lens group moving frame 18 with asufficient degree of precision since the first lens group moving frame18 is slidably fitted into the cam ring 15. The first lens group movingframe 18 is provided, on an inner peripheral surface thereof atequi-angular intervals in a circumferential direction thereof, with theset of three linear guide grooves 18 c which extend parallel to theoptical axis O.

[0076] The second lens group moving frame 19 is fitted in the first lensgroup moving frame 18. The second lens group moving frame 19 isprovided, on an outer peripheral surface thereof at the front end of theouter peripheral surface, with the set of three linear guide keys 19 awhich are slidably engaged into the set of three linear guide grooves 18c of the first lens group moving frame 18, respectively.

[0077] As shown in FIGS. 5, 6 and 7, the second lens group L2 includesthree lens elements: front, middle and rear lens elements. The frontlens element is fixed to the second lens group moving frame 19 to bedirectly supported thereby. The rear lens element is supported by asupport ring 19 d which is fixed to the second lens group moving frame19 from rear thereof, so that the rear lens element is supported by thesecond lens group moving frame 19 via the support ring 19 d. The middlelens element is fixed to the rear lens element so that a rear surface ofthe middle lens element is cemented to a front surface of the rear lenselement. Accordingly, the middle lens element of the second lens groupL2 is supported by the second lens group moving frame 19 via the rearlens element of the second lens group L2 and the support ring 19 d.

[0078] As can be understood from the above description, according to theabove described guiding mechanisms of the zoom lens barrel 1, the outerring 16 is guided linearly in the optical axis direction withoutrotating about the optical axis O via the stationary ring 13, the innerring 17 is guided linearly in the optical axis direction withoutrotating about the optical axis O via the outer ring 16, the first lensgroup moving frame 18 is guided linearly in the optical axis directionwithout rotating about the optical axis O via the inner ring 17, and thesecond lens group moving frame 19 is guided linearly in the optical axisdirection without rotating about the optical axis O via the first lensgroup moving frame 18, in that order from the outside to the inside ofthe zoom lens barrel 1. Furthermore, the linear guiding mechanismprovided between the inner ring 17 and the first lens group moving frame18 includes the set of three linear guide bosses 17 d, which extend in adirection parallel to the optical axis, and the set of three linearguide holes 18 a, and is positioned in the vicinity of the front end ofeach of the inner ring 17 and the first lens group moving frame 18. Dueto this structure, no other linear guiding elements have to be providedon either the inside or the outside of the cam ring 15. This contributesto a reduction of the annular space between the inner ring 17 and thefirst lens group moving frame 18 to thereby minimize the diameter of thezoom lens barrel 1.

[0079] As shown in FIGS. 5 through 7, the zoom lens barrel 1 is providedwith a first lens frame (lens supporting frame) 20 to which the firstlens group L1 is fixed. The first lens frame 20 is fixed to the firstlens group moving frame 18, so that the first lens frame 20 and thefirst lens group moving frame 18 constitute a front lens support member.Accordingly, the first lens group L1 is supported by the first lensgroup moving frame 18 via the first lens frame 20. More specifically,the first lens frame 20 is provided on an outer peripheral surfacethereof with a male thread portion which is in mesh with the femalethread portion 18 d of the inner flange 18 b. The first lens frame 20 iscemented to the first lens group moving frame 18 by an adhesive afterthe thread engagement position of the male thread portion of the firstlens frame 20 with respect to the female thread portion 18 d of theinner flange 18 b has been adjusted during assembly. The zoom lensbarrel 1 is provided in an annular recess 19 b of the second lens groupmoving frame 19 with a shutter unit 21 which is fixed to the second lensgroup moving frame 19 by set screws (not shown). A light shield ring 19c is fitted in the second lens group moving frame 19 from front thereofto be fixed thereto to hold the shutter unit 21 between the light shieldring 19 c and the second lens group moving frame 19. The shutter unit 21is provided with shutter blades 21 a. The shutter unit 21 drives theshutter blades 21 a to open and close in accordance with information onan object brightness. The zoom lens barrel 1 is provided therein with aflexible printed wiring board (flexible PWB) 21 b one end (front end) ofwhich is fixed to the shutter unit 21 (see FIG. 7). A drive signal isgiven to the shutter unit 21 via the flexible PWB 21 b. As shown in FIG.7, the flexible PWB 21 b extends rearward from the shutter unit 21, andsubsequently bends radially outwards to extend forward. Subsequently,the flexible PWB 21 b penetrates the stationary ring 13 via athrough-slot 28 a (see FIGS. 4 and 7) formed thereon, and bends radiallyoutwards to extend rearward along a guiding portion 28 of the stationaryring 13 which extends parallel to the optical axis O. A portion of theflexible PWB 21 b which extends along the outer surface of the guidingportion 28 is cemented thereto. Subsequently, the flexible PWB 21 bextends rearward to be positioned outside the housing 11. As shown inFIG. 7, a bending portion 21 bx of the flexible PWB 21 b in the vicinityof the through-slot 28 a passes through a rubber band 29 which is hookedover a hook 11 f formed at the rear end of the housing 11. In a statewhere the zoom lens barrel 1 is fully extended as shown below theoptical axis O in FIG. 7, the front end of the stretched rubber band 29is positioned behind the position of the through-slot 28 a in theoptical axis direction to pull the bending portion 21 bx obliquelyrearwards in a direction away from the optical axis O to prevent theflexible PWB 21 b from bending to interfere with the photographingoptical path of the zoom lens barrel 1.

[0080] The zoom lens barrel 1 is provided with a third lens frame 22 towhich the third lens group L3 is fixed. As shown in FIG. 4, the thirdlens frame 22 is guided in the optical axis direction via a pair oflinear guide rods 22 a which extend parallel to the optical axis. Thefront and rear ends of each linear guide rod 22 a are fixed to the shaftholding member 12 and the housing 11, respectively. The third lens frame22 is driven to move in the optical axis direction by rotation of a feedscrew 24 which is driven forwardly and reversely by a step motor (notshown) in accordance with information on a photographing distance.

[0081] A zooming operation is carried out by moving the first and secondlens groups L1 and L2 (the first and second lens group moving frames 18and 19) in the optical axis direction relative to the third lens groupL3 while varying the distance therebetween. The cam ring 15 is provided,on an inner peripheral surface thereof at equi-intervals in acircumferential direction of the cam ring 15, with a set of threelens-drive cam grooves C1 (see FIGS. 1, 3 and 5). The first lens groupmoving frame 18 and the second lens group moving frame 19, which areguided linearly in the optical axis direction without rotating about theoptical axis O, move in the optical axis direction by rotation of thecam ring 15 in accordance with the profiles of the lens-drive camgrooves C1. The developed view of the lens-drive cam grooves C1 is shownin FIGS. 8 through 10. In FIG. 8 each lens-drive cam groove C1, which isformed on an inner peripheral surface of the cam ring 15, is shown bydotted lines and is shown by solid lines in FIGS. 9 and 10 to clearlyindicate the profile thereof. A feature of the zoom lens barrel 1 isthat each lens-drive cam groove C1 is formed as a continuous bottomedgroove to have respective cam groove portions for the first and secondlens groups L1 and L2, and that the first and second lens groups L1 andL2 are released from the constraints of the set of three lens-drive camgrooves C1 at their respective accommodation positions so that the firstand second lens groups L1 and L2 can be accommodated to be positionedclose to each other until the first lens frame 20 and the second lensgroup moving frame 19 come into contact with each other.

[0082] Namely, the set of three follower pins 18 f that are projectedradially outwards from the first lens group moving frame 18 and the setof three follower pins 19 f that are projected radially outwards fromthe second lens group moving frame 19 are slidably engaged in the set ofthree lens-drive cam grooves C1, respectively. Each lens-drive camgroove C1, which is formed as a continuous bottomed groove, has afunction to move the first and second lens groups L1 and L2 (the firstand second lens group moving frames 18 and 19) in their respective zoompaths. Unlike the present embodiment of the zoom lens barrel 1, in aconventional zoom lens barrel having a cam ring for driving a pluralityof movable lens groups, a set of cam grooves is necessary for each ofthe plurality of movable lens groups.

[0083] Each lens-drive cam groove C1 is provided at one end thereof withan insertion end C1 e via which one of the three follower pins 18 f ofthe first lens group moving frame 18 and one of the three follower pins19 f of the second lens group moving frame 19 are inserted into thelens-drive cam groove C1. Each lens-drive cam groove C1 is furtherprovided with a first-lens-group zooming section (front lens groupmoving section) C1Z1, a second-lens-group zooming section (rear lensgroup moving section) C1Z2, a first-lens-group accommodation sectionC1A1 and a second-lens-group accommodation section C1A2, in that orderfrom the insertion end C1 e. The opposite ends (lower and upper ends asviewed in FIG. 9) of the first-lens-group zooming section C1Z1determines a telephoto extremity Z1T and a wide-angle extremity Z1W ofthe first lens group L1, respectively. The opposite ends (lower andupper ends as viewed in FIG. 9) of the second-lens-group zooming sectionC1Z2 determines a telephoto extremity Z2T and a wide-angle extremity Z2Wof the second lens group L2, respectively. As shown in FIGS. 8 through10, the width of each of the first-lens-group accommodation section C1A1and the second-lens-group accommodation section C1A2 in the optical axisdirection is greater than the width of each the first-lens-group zoomingsection C1Z1 and the second-lens-group zooming section C1Z2 so that theassociated follower pins 18 f and 19 f can move freely in thefirst-lens-group accommodation section C1A1 and the second-lens-groupaccommodation section C1A2, respectively. Namely, the first-lens-groupaccommodation section C1A1 extends in a circumferential direction of thecam ring 15, and also widens in the optical axis direction to form aclearance for the associated follower pin 18 f of the first lens groupmoving frame 18 to be movable in the optical axis direction by an amountof movement corresponding to the range of adjustment of the threadengagement position of the male thread portion of the first lens frame20 with respect to the female thread portion 18 d of the inner flange 18b. On the other hand, the second-lens-group accommodation section C1A2extends in both a circumferential direction of the cam ring 15 and theoptical axis direction to form a substantially triangular area to form aclearance for the associated follower pin 19 f of the second lens groupmoving frame 19 to be movable freely and widely in both thecircumferential direction of the cam ring 15 and the optical axisdirection within the triangular area.

[0084] The relative angular positions of the set of three follower pins18 f and the set of three follower pins 19 f about the optical axis Oare determined so that each follower pin 18 f and each follower pin 19 fare respectively positioned in the first-lens-group accommodationsection C1A1 and the second-lens-group accommodation section C1A2 whenthe cam ring 15 is positioned in an accommodation position thereof. Thefirst-lens-group accommodation section C1A1 and the second-lens-groupaccommodation section C1A2, to some extent, do not constrain movement ofthe associated follower pins 18 f and 19 f, respectively. Namely, eachfollower pin 18 f and each follower pin 19 f can move in thefirst-lens-group accommodation section C1A1 and the second-lens-groupaccommodation section C1A2, respectively, in the optical axis directionbecause of the clearance formed between each groove portion and theassociated follower pin. This clearance contributes to furtherminiaturization of the length of the zoom lens barrel 1 in anaccommodation state thereof (i.e., the distance between the first lensgroup moving frame 18 and the second lens group moving frame 19 in theoptical axis direction can be minimized since both moving frames 18 and19 are released from positioning restrictions of the cam grooves and camfollowers thereof). The amount of clearance formed between thefirst-lens-group accommodation section C1A1 and the associated followerpin 18 f is sufficient to absorb a variation in position of theassociated follower pin 18 f which is caused by an adjustment of thethread engagement position of the male thread portion of the first lensframe 20 with respect to the female thread portion 18 d of the innerflange 18 b in an accommodation state of the zoom lens barrel 1.

[0085] The inner flange 17 c of the inner ring 17 is provided with a setof three engaging protrusions 17 g (only one of which appears in FIGS.1, 3 and 5) arranged at different angular positions in a circumferentialdirection of the inner ring 17. The first lens group moving frame 18 isprovided with a set of three recesses 18 g to correspond to the set ofthree engaging protrusions 17 g. Three helical compression springs 30serving as a biasing device are inserted to be held between the set ofthree engaging protrusions 17 g and the set of three recesses 18 g,respectively, to press the first lens group moving frame 18 rearwards inthe optical axis direction. Therefore, the first lens frame 20, which issupported by the first lens group moving frame 18, can retract up to amechanical contacting point P (see FIGS. 5 and 6) where the first lensframe 20 comes in contact with the light shield ring 19 c of the secondlens group moving frame 19 due to the clearance between thefirst-lens-group accommodation section C1A1 of each lens-drive camgroove C1 of the cam ring 15 and the associated follower pin 18 f of thefirst lens group moving frame 18. By providing the helical compressionsprings 30, which have a small length, in between the inner ring 17 andthe first lens group moving frame 18, the relative movement between thefirst and second lens group moving frames 18 and 19 can be reduced,however, even if the helicoid compression springs 30 are not provided,the first and second lens group moving frames 18 and 19 can stillretract up so that the first lens frame 20 contacts the mechanicalcontacting point P. Likewise, the second lens group moving frame 19 canretract up to a mechanically contacting point Q (see FIGS. 5 and 6)where the second lens group moving frame 19 comes in contact with thethird lens frame 22 due to a clearance between the second-lens-groupaccommodation section C1A2 of each lens-drive cam groove C1 of the camring 15 and the associated follower pin 19 f of the second lens groupmoving frame 19. Due to such structures of the mechanical contactingpoints P and Q, the length of the zoom lens barrel 1 in an accommodationstate thereof is successfully reduced as compared with a conventionalzoom lens barrel in which the respective accommodation positions offirst and second lens groups which correspond to the first and secondlens groups L1 and L2 of the present embodiment of the zoom lens barrelare precisely determined by associated cam grooves. Furthermore, thethird lens frame 22 can retract up to a mechanical contacting point Rwhere it comes in contact with the housing 11 while compressing ahelical compression spring 23 (see FIGS. 1 and 4), which is positionedbetween the third lens frame 22 and the housing 11 to press the thirdlens frame 22, forward. The axial cross sectional view of the zoom lensbarrel 1 above the optical axis O in each of FIGS. 5, 6 and 7 shows anaccommodation state of the zoom lens barrel 1 where the first lens frame20 is in contact with the light shield ring 19 c of the second lensgroup moving frame 19, where the second lens group moving frame 19 is incontact with the third lens frame 22, and where the third lens frame 22is in contact with the housing 11. The amount of rearward movement ofthe first lens group moving frame 18 relative to the second lens groupmoving frame 19 depends on the position of the first lens frame 20relative to the first lens group moving frame 18 because the position ofthe first lens frame 20 relative to the first lens group moving frame 18varies by an adjustment of the thread engagement position of the malethread portion of the first lens frame 20 with respect to the femalethread portion 18 d of the inner flange 18 b during assembly. Such avariation due to the adjustment is absorbed by extension or compressionof the helical compression springs 30 so that the zoom lens barrel 1 canbe accommodated with the first lens frame 20, the second lens groupmoving frame 19 and the third lens frame 22 being in contact with thelight shield ring 19 c, the third lens frame 22 and the housing 11 atthe mechanically contacting points P, Q and R, respectively.

[0086] If the cam ring 15 rotates in a direction from the accommodationposition toward a ready-to-photograph position in a zooming sectionbetween the telephoto extremity Z1T and the wide-angle extremity Z1Wthereof, each follower pin 18 f of the first lens group moving frame 18which is engaged in the first-lens-group accommodation section C1A1moves from the first-lens-group accommodation section C1A1 to thefirst-lens-group zooming section C1Z1 via the second-lens-group zoomingsection C1Z2, while each follower pin 19 f of the second lens groupmoving frame 19 which is engaged in the second-lens-group accommodationsection C1A2 moves from the second-lens-group accommodation section C1A2to the second-lens-group zooming section C1Z2 via the first-lens-groupaccommodation section C1A1. Accordingly, the second-lens-group zoomingsections C1Z2 of the set of three lens-drive cam grooves C1 that areused for driving the set of three follower pins 19 f of the second lensgroup moving frame 19 are used as mere passing sections for the set ofthree follower pins 18 f of the first lens group moving frame 18 viawhich the set of three follower pins 18 f move from the first-lens-groupaccommodation position to the ready-to-photograph position. Theabove-described structure which provides such passing sections isadvantageous to reduce the number of cam grooves which are to be formedon the cam ring 15, which is in turn advantageous to reduce the angle ofinclination of each cam groove with respect to a circumferentialdirection of the cam ring 15.

[0087] The inner ring 17 moves in the optical axis direction independentof the first lens group moving frame 18 in a moving path which issubstantially identical to the moving path of the first lens groupmoving frame 18. Accordingly, the cam ring 15 is provided, on an outerperipheral surface at equi-intervals in a circumferential directionthereof, with a set of three cam grooves C2. The inner ring 17 isprovided, on an inner peripheral surface at equi-intervals in acircumferential direction thereof, with a set of three follower pins 17f (only one of them appears in FIG. 5) which are slidably engaged in theset of three cam grooves C2 of the cam ring 15, respectively. As can beseen in FIG. 8, the profiles of the cam grooves C2 resemble those of thelens-drive cam grooves C1. As shown in FIG. 8, each cam groove C2 isprovided at one end thereof with an insertion end C2 e via which one ofthe three follower pins 17 f of the inner ring 17 is inserted into thecam groove C2. Each cam groove C2 is further provided with a firstsection C2Z1 which corresponds to the first-lens-group zooming sectionC1Z1 , a second section C2Z2 which corresponds to the second-lens-groupzooming section C1Z2, and a barrier drive section C2B. The barrier drivesection C2B extends in a circumferential direction of the cam ring 15,so that the cam ring 15 rotates about the optical axis O without movingin the optical axis direction relative to the inner ring 17 as long aseach follower pin 17 f is engaged in the barrier drive section C2B. Ascan be clearly seen in FIG. 8, the set of three lens-drive cam groovesC1 and the set of three cam grooves C2 are formed on the cam ring 15 atslightly different positions in the optical axis direction, while theset of three follower pins 17 f that are respectively engaged in the setof three cam grooves C2 and the set of three follower pins 18 f that arerespectively engaged in the set of three lens-drive cam grooves C1 arerespectively aligned side by side in a direction parallel to the opticalaxis O.

[0088] By providing the inner ring 17, which extends forward so that anouter peripheral surface thereof is exposed to the outside of the zoomlens barrel 1, as an element separate from the first lens group movingframe 18, and by guiding the inner ring 17 in the optical axis directionvia a cam mechanism independent of the first lens group moving frame 18as described above, external forces applied to the inner ring 17 can beprevented from being transferred to the first lens group L1 via thefirst lens group moving frame 18, which in turn prevents deteriorationin optical performance of the zoom lens barrel 1 due to eccentricity ofthe optical axis of the first lens group L1. In addition, the structureof the cam ring 15 wherein the set of three lens-drive cam grooves C1and the set of three cam grooves C2, whose cam profiles are similar(though differing slightly in shape) to each other, are formed on thecam ring 15 in slightly different positions thereon in the optical axisdirection does not increase the wall thickness of the cam ring 15;moreover, external forces applied to the inner ring 17 in a directionradially inwards can be received by the first lens group moving frame 18via the set of three follower pins 18 f (i.e. the strength of the wholezoom lens barrel 1 can be reinforced). Furthermore, since the set ofthree follower pins 17 f and the set of three follower pins 18 f arerespectively aligned side by side in a direction parallel to the opticalaxis O, the strength of the spring force of the three helicalcompression springs 30 that are held between the inner ring 17 and thefirst lens group moving frame 18 to bias the inner ring 17 and the firstlens group moving frame 18 in opposite directions away from each othervaries little even if the cam ring 15 rotates relative to the inner ring17 and the first lens group moving frame 18. Namely, since the directionof the helical compression springs 30 and aligned direction of the camfollowers 17 f and 18 f are same and are parallel to the optical axis O,backlash with the cam grooves Cl and the cam followers 17 f and backlashwith the cam grooves C2 and cam followers 18 f are absorbed by thehelical compression springs 30, and accordingly, the optical performanceof the zoom lens can be reliably maintained wherever the cam followers17 f and 18 f are positioned in the cam-grooves C1 and C2 respectively.

[0089] The barrier unit 40 is fixed to an inner surface of the main ringbody 17 r to be positioned therein. The barrier drive ring 31 ispositioned in the inner ring 17 and held between the barrier unit 40 andthe inner flange 17 c of the inner ring 17 to be rotatable freely aboutthe optical axis O. The cam ring 15 is provided at the front end thereofwith a set of three recesses 15 k. The barrier drive ring 31 is providedon an outer peripheral surface thereof with a set of three engagingportions 31 a. The cam ring 15 is provided at one end (upper end asviewed in FIG. 8) of each recesses 15 k with a rotation transfer face 15d which extends parallel to the optical axis O and extends through acorresponding opening 17 z (see FIG. 7) provided on a circumferentialportion of the inner flange 17 c. If the cam ring 15 rotates about theoptical axis O in a barrier closing direction (clockwise as viewed fromthe front of the zoom lens barrel 1) with respect to the inner ring 17with the set of three follower pins 17 f being respectively engagedwithin the barrier drive sections C2B of the set of three cam grooves C2of the cam ring 15, the three rotation transfer faces 15 d firstly comeinto contact with the three engaging portions 31 a of the barrier drivering 31 and subsequently press the three engaging portions 31 a to givea rotational force to the barrier drive ring 31 to close a pair ofbarrier blades 42, respectively. As shown in FIG. 8, the set of threerecesses 15 k are formed on the cam ring 15 at portions thereon otherthan the portions where the three lens-drive cam grooves C1 and thethree cam grooves C2 are formed.

[0090] As shown in FIGS. 2 and 14, the barrier unit 40 is provided witha barrier blade support front plate 41, the pair of barrier blades 42,two torsion springs 43 and a barrier blade support rear plate 44, and isformed as a single assembly in advance. The barrier blade support frontplate 41 is provided at the center thereof with a substantiallyrectangular photographing aperture 41 a, and is further provided, on anrear surface thereof on opposite sides of the photographing aperture 41a, with two bosses 41 b, respectively, which extend rearwards. Eachbarrier blade 42 is provided at one end thereof with a hole in which oneof the two bosses 41 b is engaged so that each barrier blade 42 isrotatable about the associated boss 41 b. The two torsion springs 43bias the pair of barrier blades 42 to rotate in opposite rotationaldirections to shut the pair of barrier blades 42, respectively. The pairof barrier blades 42 are supported between the barrier blade supportfront plate 41 and the barrier blade support rear plate 44. The barrierblade support rear plate 44 is provided at the center thereof with acentral aperture 44 b (see FIG. 2) thereof which is aligned with thephotographing aperture 41 a in the optical axis direction, and isfurther provided on opposite sides of the central aperture with twoslots 44 a. As shown in FIGS. 12 and 13, each barrier blade 42 isprovided in the vicinity of the associated boss 41 b with an engagingprojection 42 a which extends rearward, toward the barrier drive ring31, to pass through the associated slot 44 a of the barrier bladesupport rear plate 44. The barrier drive ring 31 is provided on left andright sides of a central opening thereof with two drive projections 31 cwhich are respectively engaged with the two engaging projections 42 a ofthe pair of barrier blades 42. FIG. 12 shows the pair of barrier blades42 with chain lines in a closed state thereof, and FIG. 13 shows thepair of barrier blades 42 with chain lines in a fully open statethereof. FIG. 14 shows fundamental elements of the barrier unit 40 withthe barrier blade support front plate 41 removed.

[0091] The barrier drive ring 31 is biased to rotate in a direction toopen the pair of barrier blades 42 by a helical extension spring 45whose opposite ends are hooked on an engaging projection 31 b formed onthe barrier drive ring 31 and an engaging projection 17 h formed on afront surface of the inner flange 17 c of the inner ring 17. The springforce of the helical extension spring 45 is greater than the totalspring force of the two torsion springs 43. The two drive projections 31c of the barrier drive ring 31 come into contact with the two engagingprojections 42 a of the pair of barrier blades 42 to open the pair ofbarrier blades 42, respectively, when the barrier drive ring 31 is in afully rotated position thereof by the spring force of the helicalextension spring 45 (see FIG. 13). If the barrier drive ring 31 isrotated in a direction to close the pair of barrier blades 42 againstthe spring force of the helical extension spring 45, the two driveprojections 31 c respectively move away from the two engagingprojections 42 a of the pair of barrier blades 42 so that the pair ofbarrier blades 42 are closed by the spring force of the two torsionsprings 43 (see FIG. 12).

[0092] The three rotation transfer faces 15 d of the cam ring 15respectively come into contact with the three engaging portions 31 a ofthe barrier drive ring 31 to press the three engaging portions 31 aagainst the spring force of the helical extension spring 45 to rotatethe barrier drive ring 31. When the cam ring 15 is in the accommodationposition thereof, the three rotation transfer faces 15 d arerespectively in contact with the three engaging portions 31 a of thebarrier drive ring 31 via three through-slots 17 z formed on the innerflange 17 c of the inner ring 17. The barrier drive ring 31 is rotatedabout the optical axis O against the spring force of the helicalextension spring 45 to close the pair of barrier blades 42. If the camring 15 rotates about the optical axis O in a barrier opening direction(counterclockwise as viewed from the front of the zoom lens barrel 1)with respect to the inner ring 17 with the set of three follower pins 17f being respectively engaged within the barrier drive sections C2B ofthe set of three cam grooves C2 of the cam ring 15, the three rotationtransfer faces 15 d are respectively disengaged from the three engagingportions 31 a of the barrier drive ring 31 so that the barrier drivering 31 is rotated in a direction to open the pair of barrier blades 42by the spring force of the helical extension spring 45.

[0093]FIG. 16 shows the movement of the three rotation transfer faces 15d of the cam ring 15 in the case where the cam ring 15 rotates so thateach follower pin 15 b, which is engaged in the associated cam slot 13 bof the stationary ring 13, moves from the linear slot portion 13 b 1 tothe state-changing slot portion 13 b 2 of the associated cam slot 13 b,i.e., from the accommodation position to the preparation section (seeFIG. 11). Due to the engagement of the set of three follower pins 15 bof the cam ring 15 with the set of three cam slots 13 b and the set ofthree rotation transfer grooves 14 a, the cam ring 15 firstly rotatesabout the optical axis O while moving in the optical axis direction(each rotation transfer face 15 d moves from a position “1-1” to aposition “4-4” via positions “2-2” and “3-3” in FIG. 16), andsubsequently rotates about the optical axis O without moving in theoptical axis direction (each rotation transfer face 15 d moves from theposition “4-4” to a position “5-5” in FIG. 16). When moving from theposition “4-4” to the position “5-5”, the three rotation transfer faces15 d of the cam ring 15 are respectively disengaged from the threeengaging portions 31 a of the barrier drive ring 31 to thereby open thepair of barrier blades 42 by the spring force of the helical extensionspring 45. Conversely, if the cam ring 15 rotates so that each followerpin 15 b moves from the preparation section to the accommodationposition, the movement of each rotation transfer face 15 d from theposition “5-5” to the position “4-4” causes the pair of barrier blades42 to close.

[0094] Each of the pair of barrier blades 42 is formed as asubstantially plane plate, and is provided on a rear face thereof with asemi-circular concave face 42 b (see FIGS. 5, 6 and 17) so that the rearface of each barrier blade 42 does not come in contact with a frontmostsurface (convex surface) L1 r of the first lens group L1. The twosemi-circular concave faces 42 b together form a circular concave facethe shape of which corresponds to the shape of a central portion of theconvex frontmost surface L1 r of the first lens group L1 in a statewhere the pair of barrier blades 42 are closed. The curvature of eachsemi-circular concave face 42 b is determined to corresponds to thecurvature of the frontmost surface L1 r of the first lens group L1. Theconcave faces 42 b of the pair of barrier blades 42 make it possible toretreat the inner ring 17 to a rearward limit when the inner ring 17 isaccommodated. The concave face 42 b is formed on each barrier blade 42when the barrier blades 42 are molded of synthetic resin.

[0095] After the reinforcing ring 17 x is fitted on and adhered to themain ring body 17 r, the barrier unit 40 having the above describedstructure is fitted into the reinforcing ring 17 x from the frontthereof. The barrier blade support front plate 41 is provided on anouter peripheral edge thereof with a plurality of engaging portionswhich are respectively engaged with a corresponding plurality of hooksformed on an inner peripheral surface of the main ring body 17 r infront of the inner flange 17 c to prevent the barrier unit 40 fromcoming off the front of the inner ring 17. The barrier drive ring 31 isheld between the barrier unit 40 and the inner flange 17 c of the innerring 17 to be rotatable about the optical axis O. The main ring body 17r, which is made of synthetic resin, is provided, at the front endthereof on opposite sides of the central circular opening of the mainring body 17 r, with two cutout portions 17 k (see FIG. 14) in whichrespective outer edges of the pair of barrier blades 42 enter when thepair of barrier blades 42 are fully opened as shown in FIG. 14. Theradially outer ends of the two cutout portions 17 k are fully covered bythe reinforcing ring 17 x. The main body ring 17 r can be provided withthe two cutout portions 17 k each formed as a through hole in a radialdirection of the inner ring 17 due to the structure wherein the innerring 17 is constructed from two separate elements: thesynthetic-resin-made main body ring 17 r and the metal reinforcing ring17 x. Conventionally, if a set of barrier blades such as the pair ofbarrier blades 42 of the zoom lens barrel 1 is designed to consist offour blades, the total thickness of the four blades in the optical axisdirection increases though the radial width of each blade is reduced.Conversely, if the set of barrier blades is designed to consist of oneor two barrier blades, though the total thickness of the blade or bladesin the optical axis direction is reduced, the radial width of each bladeincreases. However, in the present embodiment of the zoom lens barrel 1,the formation of the two cutout portions 17 k on the main body ring 17 rthat serve as recesses for the pair of barrier blades 42 contributes tofurther miniaturization of the diameter of the inner ring 17 withoutincreasing the total thickness of the barrier blades 42 in the opticalaxis direction.

[0096] As has been described above, the zooming slot portion 13 b 3 ofeach cam slot 13 b of the stationary ring 13 extends in acircumferential direction of the stationary ring 13 and does not extendin the optical axis direction. Therefore, the set of three follower pins15 b of the cam ring 15 rotate about the optical axis O without movingin the optical axis direction when following the zooming slot portions13 b 3 of the set of three cam slots 13 b in the zooming section (seeFIG. 11). The zoom lens barrel 1 is provided between the housing 11 andthe rotatable ring 14 with a biasing ring 32 which is fitted on a frontpart of the rotatable ring 14 to remove backlash and play between theset of three follower pins 15 b and the zooming slot portions 13 b 3 ofthe set of three cam slots 13 b. The biasing ring 32 and the rotatablering 14 are provided with three hooks 32 a and corresponding three hooks14 c, respectively. Opposite ends of three helical extension springs 33are hooked on the three hooks 32 a and the three hooks 14 c,respectively, to constantly bias the biasing ring 32 rearwards in theoptical axis direction. The biasing ring 32 is provided, on an innerperipheral surface thereof at equi-angular intervals in acircumferential direction of the biasing ring 32, with a set of threeinward projections 32 c which extend radially inwards, while therotatable ring 14 is provided in the vicinity of the front end thereofwith a corresponding set of three through-slots 14 d which extendparallel to the optical axis O so that the set of three inwardprojections 32 c penetrate the rotatable ring 14 via the set of threethrough-slots 14 d in radially inward directions, respectively. The setof three throughslots 14 d are formed on the rotatable ring 14 so as tobe communicatively connected in front portions of the set of threerotation transfer grooves 14 a to penetrate therethrough, so that theset of three inward projections 32 c are positioned in front of the setof three follower pins 15 b that are engaged in the set of threerotation transfer grooves 14 a, respectively. If each follower pin 15 bof the cam ring 15 moves from the state-changing slot portion 13 b 2 tothe zooming slot portion 13 b 3, respective rear faces of the set ofthree inward projections 32 c come into pressing contact with the set ofthree follower pins 15 b to press each follower pin 15 b rearward in theoptical axis direction against the rear side edge of the associatedzooming slot portion 13 b 3 to thereby remove backlash and play betweenthe set of three follower pins 15 b and the zooming slot portions 13 b 3of the set of three cam slots 13 b.

[0097] In addition to the above described structures wherein the set ofthree linear guide grooves 18 c are formed on an inner peripheralsurface of the first lens group moving frame 18 while the set of threelinear guide keys 19 a, which are respectively engaged in the set ofthree linear guide grooves 18 c, are formed on an outer peripheralsurface of the second lens group moving frame 19, a set of threecircumferential recesses 18 h are formed on the first lens group movingframe 18 at the front ends of the set of three linear guide grooves 18c, respectively. Each circumferential recess 18 h allows the associatedlinear guide key 19 a of the second lens group moving frame 19 to movetherein in a circumferential direction about the optical axis O, i.e.,allows the second lens group moving frame 19 to rotate about the opticalaxis O relative to the first lens group moving frame 18 in a rangecorresponding to the circumferential length of the circumferentialrecess 18 h. The second lens group moving frame 19 can rotate about theoptical axis O relative to the first lens group moving frame 18 alongthe three circumferential recesses 18 h only when the second lens groupmoving frame 19 is in the vicinity of the accommodation positionthereof. The first lens group moving frame 18 is provided on the innerflange 18 b thereof with a set of three circumferential slots 18 j (seeFIGS. 3 and 6). The second lens group moving frame 19 is provided at thefront end thereof with a set of three front projecting portions 19 e onrespective outer surfaces of which the three linear guide keys 19 a areformed, respectively. When each linear guide key 19 a is positioned inthe associated circumferential recess 18 h, i.e., when the second lensgroup L2 is in the vicinity of the accommodation position thereof, theset of three front projecting portions 19 e of the second lens groupmoving frame 19 penetrates through the inner flange 18 b of the firstlens group moving frame 18 to project forward from the inner flange 18 bvia the set of three circumferential slots 18 j, respectively.Accordingly, by allowing the three linear guide keys 19 a to projectforward from the inner flange 18 b through the three circumferentialslots 18 j, respectively, the length in the optical axis direction ofthe three linear guide grooves 18 c and the circumferential recesses 18h which reliably carry out the engaging and disengaging of the threelinear guide keys 19 a with the three linear guide grooves 18 c, and theamount of movement of the first and second lens group moving frames 18and 19 in the optical axis direction can be maintained withoutincreasing the combined length of the first and second lens group movingframes 18 and 19 at the accommodation positions thereof. The reason whythe second lens group moving frame 19 is allowed to rotate relative tothe first lens group moving frame 18 along the three circumferentialrecesses 18 h only when the second lens group moving frame 19 is in thevicinity of the accommodation position thereof will be hereinafterdiscussed.

[0098] In a state where the zoom lens barrel 1 is in an accommodationstate, i.e., where each of the set of three follower pins 18 f of thefirst lens group moving frame 18 is engaged in the first-lens-groupaccommodation section C1A1 of the associated lens-drive cam groove C1, arotation of the cam ring 15 in a direction to extend the zoom lensbarrel 1 (in a direction indicated by an arrow “X” in FIG. 10, i.e.,counterclockwise as viewed from the front of the zoom lens barrel 1)causes each follower pin 18 f of the first lens group moving frame 18 tomove from the first-lens-group accommodation section C1A1 to thesecond-lens-group zooming section C1Z2 of the associated lens-drive camgroove C1, to thereby cause the first lens group moving frame 18 to moveforward in the optical axis direction. Such a movement of each followerpin 18 f of the first lens group moving frame 18 is indicated stepwiseby first, second, third and fourth positions “1a”, “2a”, “3a” and “4a”in FIG. 10. Likewise, the corresponding movement of each follower pin 19f of the second lens group moving frame 19 is indicated stepwise byfirst, second, third and fourth positions “1b”, “2b”, “3b” and “4b” inFIG. 10, while the corresponding movement of each linear guide key 19 aof the second lens group moving frame 19 is indicated stepwise by first,second, third and fourth positions “1c”, “2c”, “3c” and “4c” in FIG. 10.

[0099] In addition, such a rotation of the cam ring 15 in the directionX shown in FIG. 10 causes each follower pin 19 f of the second lensgroup moving frame 19 which is positioned in the second-lens-groupaccommodation section C1A2 of the associated lens-drive cam groove C1 tomove from the position “1b” to the position “2b” in thesecond-lens-group accommodation section C1A2 to come into contact with asurface XX of an inclined side edge of the second-lens-groupaccommodation section C1A2 which is inclined with respect to acircumferential direction of the cam ring 15. The position “2b” in thesecond-lens-group accommodation section C1A2 is positioned on theinclined side edge β of the second-lens-group accommodation sectionC1A2.

[0100] A further rotational movement of the cam ring 15 in the samedirection X causes each follower pin 19 f of the second lens groupmoving frame 19 to slide on the surface XX of the inclined side edge βin a direction inclined to both the optical axis direction and thecircumferential direction of the cam ring 15 in a manner such as thefollowing.

[0101] At this time, each linear guide key 19 a is in contact with aside surface (the lower surface as viewed in FIG. 10) of the associatedcircumferential recess 18 h of the first lens group moving frame 18 (seethe position “2c” of the linear guide key 19 a shown in FIG. 10).Therefore, a forward movement of the first lens group moving frame 18 inthe optical axis direction causes the first lens group moving frame 18to push the second lens group moving frame 19 forward in the opticalaxis direction via the circumferential recesses 18 h and the set ofthree linear guide keys 19 a, and at the same time, causes the secondlens group moving frame 19 to rotate about the optical axis O relativeto the first lens group moving frame 18 due to the sliding movement ofeach follower pin 19 f of the second lens group moving frame 19 on thesurface XX of the inclined side edge β from the position “2b” to theposition “3b”. Namely, each linear guide key 19 a moves from theassociated circumferential recess 18 h toward the associated linearguide groove 18 c while sliding on the side surface (the lower surfaceas viewed in FIG. 10) of the associated circumferential recess 18 h.

[0102] Accordingly, if the second lens group moving frame 19 is rotatedrelative to the first lens group moving frame 18, the first lens groupmoving frame 18 can move forward smoothly without interfering with thesecond lens group moving frame 19.

[0103] Thereafter, each linear guide key 19 a comes into contact with aside edge (the right side edge as viewed in FIG. 10) of the associatedlinear guide groove 18 c of the first lens group moving frame 18 tothereby stop the rotation of the second lens group moving frame 19 (seethe position “3c”). At this time, each linear guide key 19 a is ready toenter the associated linear guide groove 18 c of the first lens groupmoving frame 18, so that a further forward movement of the first lensgroup moving frame 18 causes the set of three linear guide key 19 a toenter the set of three linear guide grooves 18 c, respectively. Afterthe set of three linear guide keys 19 a have respectively entered theset of three linear guide grooves 18 c, the second lens group movingframe 19 is prevented from rotating about the optical axis O relative tothe first lens group moving frame 18 by engagement of each linear guidekey 19 a with the associated linear guide groove 18 c, while eachfollower pin 19 f of the second lens group moving frame 19 slides on thesurface XX of the inclined side edge β from the position “3b” to “4b”,which causes the second lens group moving frame 19 to move linearly in adirection opposite to the direction of movement of the first lens groupmoving frame 18 (see the position “4b” in FIG. 10).

[0104] Further rotational movement of the cam ring 15 causes eachfollower pin 19 f of the second lens group moving frame 19 to enter thefirst-lens-group accommodation section C1A1 of the associated lens-drivecam groove C1. Thereafter, if the cam ring 15 rotates in the directionX, the first and second lens group moving frames 18 and 19 move linearlyin the optical axis direction in accordance with the respective sectionsof the set of three lens-drive cam grooves C1 while the second lensgroup moving frame 19 is guided linearly in the optical axis directionby the first lens group moving frame 18. As can be understood from theabove description, the substantially triangular shaped second-lens-groupaccommodation section C1A2 of each lens-drive cam groove C1 not onlysecures a clearance for the associated follower pin 19 f to be movablefreely in both the circumferential direction of the cam ring 15 and theoptical axis direction within the triangular area, but also makes thesecond lens group moving frame 19 rotate relative to the first lensgroup moving frame 18 to lead each linear guide key 19 a to a positionso as to be engaged in the associated linear guide groove 18 c.Moreover, the substantially triangular shaped second-lens-groupaccommodation section C1A2 of each lens-drive cam groove C1 allows thefirst and second lens group moving frames 18 and 19 move in oppositedirections in the optical axis direction to ensure the proper engagementof the first lens group moving frame 18 with the second lens groupmoving frame 19.

[0105] On the other hand, in a state where the zoom lens barrel 1 is ina ready-to-photograph state, if the cam ring 15 rotates in a directionto retract the zoom lens barrel 1, i.e., in a direction opposite to thedirection X, each follower pin 18 f and each follower pin 19 f return tothe first-lens-group accommodation section C1A1 and thesecond-lens-group accommodation section C1A2, respectively.

[0106] The movement of each follower pin will be hereinafter discussedin detail. After passing the first-lens-group accommodation sectionC1A1, each follower pin 19 f slides on the surface of a rear side edge aof the second-lens-group accommodation section C1A2 to move rightwardwith respect to FIG. 10. Upon reaching a position on the surface of therear side edge a immediately before an end al (the upper end as viewedin FIG. 9) thereof, each linear guide key 19 a comes out of theassociated linear guide groove 18 c to enter the associatedcircumferential recess 18 h, to thereby allow rotation of the secondlens group moving frame 19 relative to the first lens group moving frame18 possible. Thereafter, each follower pin 19 f reaches the end α1 ofthe rear side edge a to rotate about the optical axis O together withthe cam ring 15, namely, the second lens group moving frame 19 rotatesabout the optical axis O relative to the first lens group moving frame18. Thereafter, since the cam ring 15 retreats in the optical axisdirection (in the rightward direction with respect to FIG. 9) due to theengagement of the set of three follower pins 15 b with the linear slotportions 13 b 1 of the set of three cam slots 13 b of the stationaryring 13, each follower pin 19 f finally reaches a terminal α2 in thevicinity of the end al of the rear side edge α. In this manner, thefirst and second lens group moving frames 18 and 19 move to therespective accommodation positions smoothly.

[0107] Assuming that the second lens group moving frame 19 is moved tothe accommodation position thereof with the second lens group movingframe 19 being guided only linearly in the optical axis direction in amanner similar to that of the first lens group moving frame 18, each ofthe three lens-drive cam grooves C1 has to be formed longer in acircumferential direction of the cam ring 15 (i.e., in an upwarddirection from the end α1 of the rear side edge a as viewed in FIG. 9).However, if the set of three lens-drive cam grooves C1 are simply formedlonger, theses grooves interfere with other cam grooves (e.g., the camgrooves C2). To prevent this problem from occurring, the diameter of thecam ring 15 has to be increased. However, according to the presentembodiment of the zoom lens barrel 1, the portion of each of the threelens-drive cam groove C1 which is used to accommodate the second lensgroup moving frame 19 can be designed short in a circumferentialdirection of the cam ring 15 within a range in which none of the threelens-drive cam grooves C1 interfere with other cam grooves. Thiscontributes to further miniaturization of the diameter of the cam ring15.

[0108] Since the second-lens-group accommodation section C1A2 of eachlens-drive cam groove C1 is formed having a substantially triangularshape, each lens-drive cam groove C1 is successfully formed as a shortcam groove, which would need to be longer if formed as a linear camgroove. In addition, by forming each lens-drive cam groove C1 as a shortgroove in such a manner, the set of three lens-drive cam grooves C1 canbe formed on the cam ring 15 with little inclination with respect to thecircumferential direction of the cam ring 15. Additionally, when thefirst and second lens group moving frames 18 and 19 move forward fromthe respective accommodation positions in the optical axis direction,each follower pin 19 f moves in the second-lens-group accommodationsection C1A2 from the position “1b” to the position “4b” via thepositions “2b” and “3b” in the above described manner while the secondlens group moving frame 19 rotates about the optical axis O relative tothe first lens group moving frame 18 because each lens-drive cam grooveC1 is provided with the substantially triangular shape second-lens-groupaccommodation section C1A2.

[0109]FIG. 15 shows the variation in the respective axial positions offirst and second lens group moving frames 18 and 19 in a range ofmovement including a zooming section (between telephoto extremity andwide-angle extremity) and a retracting section (between wide-angleextremity and accommodation position). As can be understood from FIG.15, the axial position of the first lens group moving frame 18corresponds to the rotational position (angular position) of the camring 15 about the optical axis O due to the profile of each lens-drivecam groove C1, while the second lens group moving frame 19 rotates aboutthe optical axis O relative to the cam ring 15 in a range R shown inFIG. 15.

[0110] Friction produced between the light shield ring 19 c of thesecond lens group moving frame 19 and the first lens frame 20 becomes aproblem if the second lens group moving frame 19 rotates relative to thefirst lens group moving frame 18 in the accommodation position becausethe first lens frame 20, which is supported by the first lens groupmoving frame 18, is in contact with the light shield ring 19 c at themechanically contacting point P (see FIGS. 5 and 6). Such friction maycause the first lens frame 20 to rotate relative to the first lens groupmoving frame 18 to thereby deviate in the optical axis directionrelative to the first lens group moving frame 18 because the male threadportion of the first lens frame 20 is in mesh with the female threadportion 18 d of the inner flange 18 b. To prevent such deviation of theaxial position of the first lens frame 20 from occurring, the lightshield ring 19 c is provided, on a front surface thereof with which arear face of the first lens frame 20 comes into contact, with alow-frictional sheet 26 (see FIGS. 5, 6 and 7) which can be made of,e.g., a tetrafluoroethylene resin.

[0111] The overall movement of the zoom lens barrel 1, having the abovedescribed structure, from the accommodation position to aready-to-photograph position (a position in the zooming section) will behereinafter discussed. When the zoom lens barrel 1 is in anaccommodation state, the first lens frame 20 which is supported by thefirst lens group moving frame 18, which is biased rearward by the threehelical compression springs 30, is retracted to the mechanicallycontacting point P where the first lens frame 20 comes in contact withthe light shield ring 19 c of the second lens group moving frame 19 dueto the clearance between the first-lens-group accommodation section C1A1of each lens-drive cam groove C1 of the cam ring 15 and the associatedfollower pin 18 f of the first lens group moving frame 18. The secondlens group moving frame 19 is also retracted to the mechanicallycontacting point Q where the second lens group moving frame 19 comes incontact with the third lens frame 22 due to the clearance between thesecond-lens-group accommodation section C1A2 of each lens-drive camgroove C1 of the cam ring 15 and the associated follower pin 19 f of thesecond lens group moving frame 19. Furthermore, the third lens frame 22is retracted to the mechanically contacting point R wherein the thirdlens frame 22 comes in contact with the housing 11 by the spring forceof the helical compression spring 23 which presses the third lens frame22 forward. With these three mechanical contacts at the mechanicallycontacting points P, Q and R, the length of the zoom lens barrel 1 in anaccommodation state of the zoom lens barrel 1 is successfully reduced.When the zoom lens barrel 1 is in an accommodation state, the pair ofbarrier blades 42 are closed to shut the photographing aperture 41 a(see FIG. 12), since the three rotation transfer faces 15 d respectivelypress the three engaging portions 31 a of the barrier drive ring 31against the spring force of the helical extension spring 45 to rotatethe barrier drive ring 31 in a direction to move the two driveprojections 31 c away from the two engaging projections 42 a of the pairof barrier blades 42, respectively.

[0112] In the accommodation state of the zoom lens barrel 1, if therotatable ring 14 rotates in a direction to extend the zoom lens barrel1 relative to the stationary ring 13, the cam ring 15 which is providedwith the set of three follower pins 15 b, moves in the optical axisdirection without rotating about the optical axis O due to theengagement of the follower pins 15 b of the cam ring 15 with theinclined groove portions 14 a 2 of the rotatable ring 14 and the linearslot portions 13 b 1 of the stationary ring 13 (see FIG. 11). Thislinear movement of the cam ring 15 causes a side edge of thefirst-lens-group accommodation section C1A1 of each lens-drive camgroove C1 to push the associated follower pin 18 f forward, and at thesame time, causes a side edge of the second-lens-group accommodationsection C1A2 of each lens-drive cam groove C1 to push the associatedfollower pin 19 f forward. As a result, the first lens frame 20 and thesecond lens group moving frame 19 (the light shield ring 19 c) which arein contact with each other at the mechanically contacting point P movelinearly forward to release the contact therebetween, while the secondlens group moving frame 19 which is in contact with the third lens frame22 at the mechanically contacting point Q moves forward linearly torelease the contact between the second lens group moving frame 19 withthe third lens group L3.

[0113] If the rotatable ring 14 further rotates in the same direction toextend the zoom lens barrel 1 relative to the stationary ring 13, thecam ring 15 moves in the optical axis direction while rotating about theoptical axis O due to the engagement of the follower pins 15 of the camring 15 with the linear groove portions 14 a 1 of the rotatable ring 14and the state-changing slot portions 13 b 2 of the stationary ring 13,until the rotatable ring 14 reaches the zooming section. In an earlystate of this rotation of the cam ring 15 by the state-changing slotportions 13 b 2 of the stationary ring 13, the three rotation transferfaces 15 d of the cam ring 15 are respectively disengaged from the threeengaging portions 31 a of the barrier drive ring 31 so that the barrierdrive ring 31 is rotated in a direction to open the pair of barrierblades 42 by the spring force of the helical extension spring 45 againstthe spring force of the two torsion springs 43. Accordingly, the secondlens group moving frame 19 rotates about the optical axis O relative tothe first lens group moving frame 18 so that the first lens frame 20slides on the low-frictional sheet 26 before and after the openingoperation of the pair of barrier blades 42.

[0114] When each follower pin 15 b of the cam ring 15 reaches thezooming slot portion 13 b 3 of the associated cam slot 13 b by rotationof the rotatable ring 14 in the same rotational direction, rear faces 32b of the set of three inward projections 32 c of the biasing ring 32come into contact with the set of three follower pins 15 b of the camring 15, respectively (see the zoom lens barrel 1 below the optical axisO in FIG. 7). Each follower pin 15 b is pressed against the rear sideedge of the zooming slot portion 13 b 3 of the associated cam slot 13 bby the rear face 32 b of the associated inward projection 32 c since thebiasing ring 32 is biased rearward by the three helical extensionsprings 33. This state is maintained as long as each follower pin 15 bis engaged in the zooming slot portion 13 b 3 of the associated cam slot13 b, while backlash and play of the cam ring 15 with respect to thestationary barrel 13 is removed as long as the cam ring 15 rotateswithin the zooming section shown in FIG. 11 via the rotatable ring 14.

[0115] If the cam ring 15 rotates in a direction from the accommodationrotational position to the zooming section via the preparation section(i.e., in the barrier opening direction), each follower pin 18 f of thefirst lens group moving frame 18 which is engaged in thefirst-lens-group accommodation section C1A1 moves from thefirst-lens-group accommodation section C1A1 to the first-lens-groupzooming section C1Z1 via the second-lens-group zooming section C1Z2,while each follower pin 19 f of the second lens group moving frame 19which is engaged in the second-lens-group accommodation section C1A2moves from the second-lens-group accommodation section C1A2 to thesecond-lens-group zooming section C1Z2 via the first-lens-groupaccommodation section C1A1. If the cam ring 15 rotates in the zoomingrange (i.e., in the first-lens-group zooming section C1Z1 and thesecond-lens-group zooming section C1Z2), the first and second lens groupmoving frames 18 and 19 (the first and second lens groups L1 and L2)move in the optical axis direction in respective zoom paths thereof inaccordance with the profiles of the first-lens-group zooming sectionC1Z1 and the second-lens-group zooming section C1Z2, to thereby vary thefocal length of the photographing optical system which includes thefirst, second and third lens groups L1, L2 and L3, i.e. , to perform azooming operation. This zooming operation is carried out by manuallyoperating a conventional zoom switch (not shown). Immediately after arelease button is depressed, the aforementioned step motor (not shown),which drives feed screw 24 to move the third lens frame 22 (the thirdlens group L3), rotates by an amount of rotation corresponding toinformation on a photographing distance to move the third lens group Lto bring an object into focus. The shutter unit 21 drives the shutterblades 21 a to open and close in accordance with the information on theobject brightness.

[0116] If the first lens group moving frame 18 moves linearly in theoptical axis direction, the inner ring 17 also moves in the optical axisdirection without varying the position thereof relative to the firstlens group moving frame 18 due to the engagement of the set of threefollower pins 17 f with the set of three cam grooves C2 of the cam ring15, the profiles of which are similar to those of the lens-drive camgrooves C1. At the same time, the outer ring 16 and the inner ring 17,the respective outer peripheral surfaces of which are exposed to theoutside of the zoom lens barrel 1, move together in the optical axisdirection since the outer ring 16 moves together with the cam ring 15 inthe optical axis direction at all times due to the engagement of the setof three bayonet prongs 16 d with the circumferential groove 15 c.

[0117] If the cam ring 15 rotates in a direction from the zoomingsection via the preparation section (i.e., in the barrier closingdirection), the outer and inner rings 16 and 17 retract together in theoptical axis direction by operations reverse to the above describedoperations. Subsequently, the first lens frame 20, which supports thefirst lens group L1, and the second lens group moving frame 19, whichsupports the second lens group L2, come into contact with each other attheir respective rear ends via the three helical compression springs 30,while the second lens group moving frame 19 retreats until coming intocontact with the third lens frame 22 to push the third lens frame 22against the filter holding portion 11 c against the helical compressionspring 23, which presses the third lens frame 22 forward. At the sametime, the three rotation transfer faces 15 d respectively press thethree engaging portions 31 a of the barrier drive ring 31 against thespring force of the helical extension spring 45 to rotate the barrierdrive ring 31 in a direction to close the pair of barrier blades 42 toshut the photographing aperture 41 a.

[0118] In the present embodiment of the zoom lens barrel 1, as describedabove, the second-lens-group zooming sections C1Z2 of the set of threelens-drive cam grooves C1, which are used for driving the set of threefollower pins 19 f of the second lens group moving frame 19, aredesigned as mere passing sections for the set of three follower pins 18f of the first lens group moving frame 18 via which the set of threefollower pins 18 f move from the first-lens-group accommodation positionto a ready-to-photograph position in a zooming section between thetelephoto extremity Z1T and the wide-angle extremity Z1W, so that eachof the three follower pins 18 f and the corresponding one of the threefollower pins 19 f are fitted in a single lens-drive cam groove of thethree lens-drive cam grooves C1. This construction contributes to areduction of the number of cam grooves to be formed on the cam ring 15,which in turn contributes to a reduction of the angle of inclination ofthe cam grooves with respect to a circumferential direction of the camring 15.

[0119] In addition, since the first lens group moving frame 18 is biasedrearward by the three helical compression springs 30, the first lensframe 20, which is supported by the first lens group moving frame 18positioned at the accommodation position thereof, can retract up to apoint (the mechanically contacting point P) where the first lens frame20 comes in contact with the light shield ring 19 c of the second lensgroup moving frame 19 due to the clearance between the first-lens-groupaccommodation section C1A1 of each lens-drive cam groove C1 of the camring 15 and the associated follower pin 18 f of the first lens groupmoving frame 18. Likewise, the second lens group moving frame 19 canretract up to a point (the mechanically contacting point Q) where thesecond lens group moving frame 19 comes in contact with the third lensframe 22 due to the clearance between the second-lens-groupaccommodation section C1A2 of each lens-drive cam groove C1 of the camring 15 and the associated follower pin 19 f of the second lens groupmoving frame 19. Due to such structures having the mechanicallycontacting points P and Q, the length of the zoom lens barrel 1 in anaccommodation state thereof is successfully reduced as compared with aconventional zoom lens barrel in which the respective accommodationpositions of first and second lens groups which correspond to the firstand second lens groups L1 and L2 of the present embodiment of the zoomlens barrel are precisely determined by associated cam grooves.

[0120] The axial cross sectional view of the zoom lens barrel 1 abovethe optical axis O in each of FIGS. 5, 6 and 7 shows an accommodationstate of the zoom lens barrel 1 where the first lens frame 20 is incontact with the light shield ring 19 c of the second lens group movingframe 19, where the second lens group moving frame 19 is in contact withthe third lens frame 22 and where the third lens frame 22 is in contactwith the housing 11. The amount of rearward movement of the first lensgroup moving frame 18 depends on the position of the first lens frame 20because the position of the first lens frame 20 relative to the firstlens group moving frame 18 varies due to an adjustment of the threadengagement position of the male thread portion of the first lens frame20 with respect to the female thread portion 18 d of the inner flange 18b during assembly. Such a variation due to the adjustment is absorbed byextension or compression of the helical compression springs 30 so thatthe zoom lens barrel 1 can be accommodated with the first lens frame 20,the second lens group moving frame 19 and the third lens frame 22 beingin contact with the light shield ring 19 c, the third lens frame 22 andthe housing 11 at the mechanically contacting points P, Q and R,respectively.

[0121] Moreover, although the first lens frame 20 and the second lensgroup moving frame 19 abut against each other, the first lens group L1and the second lens group L2 do not abut against each other. Therefore,there is no chance of forming any scratch on either the rearmost surfaceof the first lens group L1 or the frontmost surface of the second lensgroup L2.

[0122] Furthermore, since the first lens frame 20 is brought intocontact with the second lens group moving frame 19, it is not necessaryto secure a marginal space between the first and second lens groups L1and L2 for making an adjustment to the fixing position of the first lensframe 20 relative to the first lens group moving frame 18 in the opticalaxis direction, wherein the marginal space corresponds to the amount ofthread engagement of the first lens frame 20 with the first lens groupmoving frame 18. This contributes to further miniaturization of thelength of the zoom lens barrel 1 in an accommodation state thereof.

[0123] Although the first and second lens groups L1 and L2 areaccommodated with the first lens frame 20 being in contact with thesecond lens group moving frame 19 in the present embodiment of the zoomlens barrel 1, the first and second lens groups L1 and L2 can beprovided with a contacting surface of the first lens group L1 being incontact with a corresponding contacting surface of the second lens groupL2 if such two contacting surfaces are respectively formed on the firstand second lens groups L1 and L2.

[0124] When the first lens frame 20, the second lens group moving frame19 and the third lens frame 22 are positioned at their respectiveaccommodation positions, the frontmost surface L1 r of the first lensgroup L1 does not come into contact with the pair of barrier blades 42because each of the pair of barrier blades 42 is provided on a rear facethereof with the concave face 42 b even, if the frontmost lens elementof the first lens group L1 slightly moves back and forth due tocontraction/expansion of the helical compression springs 30.

[0125] The above described linear guiding mechanism for guiding thefirst and second lens group moving frames 18 and 19 in the optical axisdirection without rotating about the optical axis O is not limitedsolely to such a particular mechanism as long as the general concept ofthe set of lens-drive cam grooves C1 is applied.

[0126] Although the set of three lens-drive cam grooves C are formed onthe cam ring 15 in the above illustrated embodiment of the zoom lensbarrel 1, a similar effect can in theory be expected with only onelens-drive cam groove C1.

[0127] The present invention can be applied not only to a extendablezoom lens barrel, the axial length of which in an accommodation statebeing generally difficult to be minimized, but also to a extendablefixed-focal-length lens barrel having a plurality of movable lensgroups.

[0128] As can be understood from the foregoing, according to a lensbarrel to which the present invention is applied, since a follower pinfor moving a lens group and another follower pin for moving another lensgroup can be engaged in a single cam groove, the number of cam grooveswhich are to be formed on a cam ring can be minimized even if the lensbarrel is provided with a large number of movable lens groups.Accordingly, the cam ring does not need to have a large diameter, andthe cam ring can be provided with cam grooves which ensure smoothmovements of the associated follower pins while keeping a decrease instrength of the cam ring to a minimum.

[0129] Moreover, each of a plurality of lens groups provided in the lensbarrel can be accommodated as compact as possible while preventingadjacent lens groups from contacting each other, even if the lens barrelis of a type wherein at least one lens group is fixed to the lenssupport frame thereof while the fixing position of the lens group isbeing adjusted relative to the lens support frame thereof in the opticalaxis direction, or even if the lens barrel is of a extendable lensbarrel provided at the front end thereof with a photographing apertureand a lens barrier which opens and closes the photographing aperture.

[0130] Furthermore, even if the zoom lens barrel having two or more lensgroups is fully retracted, these lens groups can be accommodated compactin the retracted zoom lens barrel.

[0131] Obvious changes may be made in the specific embodiment of thepresent invention described herein, such modifications being within thespirit and scope of the invention claimed. It is indicated that allmatter contained herein is illustrative and does not limit the scope ofthe present invention.

What is claimed is:
 1. A lens barrel comprising: first and second lensgroups guided in an optical axis direction without rotating about saidoptical axis; a first support frame which supports said first lensgroup, said first support frame including a first cam follower; a secondsupport frame which supports said second lens group, said second supportframe including a second cam follower; and a cam ring which is driven torotate about said optical axis, said cam ring including a cam groove inwhich said first cam follower and said second cam follower are engaged;wherein said cam groove is formed as a continuous groove and includes afirst groove portion via which said first cam follower is guided to movesaid first lens group, and a second groove portion via which said secondcam follower is guided to move said second lens group; and wherein saidcam groove is formed so that one of said first cam follower and saidsecond cam follower enters a corresponding one of said first grooveportion and said second groove portion after passing through the otherof said first groove portion and said second groove portion in apreparation stage of said lens barrel.
 2. The lens barrel according toclaim 1, wherein said first groove portion comprises: a first zoomingsection for moving said first lens group to perform a zooming operation;and a first accommodation section in which said first cam follower ispositioned when said first lens group is accommodated; wherein saidsecond groove portion comprises: a second zooming section for movingsaid second lens group to perform said zooming operation; and a secondaccommodation section in which said second cam follower is positionedwhen said first lens group is accommodated; and wherein said firstzooming section, said second zooming section, said first accommodationsection and said second accommodation section are arranged in that orderfrom one end of said cam groove, so that said first cam follower passesthrough said second zooming section when moving between said firstaccommodation section and said first zooming section.
 3. The lens barrelaccording to claim 1, wherein said first lens group is positioned infront of said second lens group.
 4. The lens barrel according to claim3, wherein each of said first lens group and said second lens groupconstitutes a lens element of a zoom lens optical system, said cam ringbeing driven to move said first lens group and said second lens group insaid optical axis direction while changing a distance therebetween tovary a focal length.
 5. The lens barrel according to claim 3, furthercomprising a third lens group positioned behind said second lens groupand guided in said optical axis direction, wherein said third lens groupconstitutes a focusing lens and is moved in said optical axis directionto perform a focusing operation.
 6. A lens barrel comprising: a frontlens support member which supports a front lens group and is guided inan optical axis direction without rotating about said optical axis; arear lens support member which supports a rear lens group and is guidedin said optical axis direction without rotating about said optical axis;and a support frame movement mechanism for moving said front lenssupport member and said rear lens support member between respectiveready-to-photograph positions and respective accommodation positionslocated behind said respective ready-to-photograph positions, in saidoptical axis direction; wherein said support frame movement mechanismbrings said front lens support member and said rear lens support memberinto contact with each other at said respective accommodation positionswithout causing said front lens group and said second lens group to comeinto contact with each other.
 7. The lens barrel according to claim 6,wherein said support frame movement mechanism comprises a biasingdevice; and wherein said support frame movement mechanism brings saidfront lens support member and said rear lens support member into contactwith each other, with a biasing force of said biasing device, at saidrespective accommodation positions.
 8. The lens barrel according toclaim 6, wherein said support frame movement mechanism comprises: afirst cam follower formed on said front lens support member; a secondcam follower formed on said rear lens support member; and a cam ringwhich is driven to rotate about said optical axis, said cam ringincluding a cam groove in which said first cam follower and said secondcam follower are engaged; wherein said cam groove comprises: a frontlens group moving section for moving said front lens support member tosaid ready-to-photograph position; a rear lens group moving section formoving said rear lens support member to said ready-to-photographposition; a front lens group accommodation section for allowing saidfront lens group to move to said accommodation position which is locatedbehind a position of said front lens group in said optical axisdirection when said first cam follower is positioned in said front lensgroup moving section; and a rear lens group accommodation section forallowing said rear lens group to move to said accommodation positionwhich is located behind a position of said rear lens group in saidoptical axis direction when said second cam follower is positioned insaid rear lens group moving section; wherein said front lens groupaccommodation section defines a clearance between said front lens groupaccommodation section and said first cam follower so that said first camfollower is movable in said optical axis direction in said front lensgroup accommodation section; and wherein said rear lens groupaccommodation section defines a clearance between said rear lens groupaccommodation section and said second cam follower so that said secondcam follower is movable in said optical axis direction in said rear lensgroup accommodation section.
 9. The lens barrel according to claim 8,wherein said front lens group moving section and said rear lens groupmoving section constitute a first zooming section and a second zoomingsection, respectively, for varying a focal length to perform a zoomingoperation.
 10. The lens barrel according to claim 7, wherein saidbiasing device biases said front lens support member in a directiontoward said accommodation position so that said front lens supportmember moves to come in contact with said rear lens support member. 11.The lens barrel according to claim 8, wherein an area of said front lensgroup accommodation section is smaller than an area of said rear lensgroup accommodation section.
 12. A lens barrel having an optical systemincluding of a plurality of lens groups, said lens barrel comprising: alens supporting frame to which a frontmost lens group of said pluralityof lens groups is supported; a first moving frame to which said lenssupporting frame is supported via male and female screw-threadedportions meshing with each other, one and the other of said male andfemale screw-threaded portions being formed on said lens supportingframe and said first moving frame, respectively; a second moving frameto which a rear lens group of said plurality of lens groups which ispositioned behind said frontmost lens group is supported; and a supportframe movement mechanism for moving said first moving frame and saidsecond moving frame between respective ready-to-photograph positions andrespective accommodation positions located behind said respectiveready-to-photograph positions in a direction of an optical axis; whereina supporting position of said lens supporting frame, relative to saidfirst moving frame in said optical axis direction, is adjusted via saidmale and female screw-threaded portions during assembly; and whereinsaid support frame movement mechanism brings said lens supporting frameand said second moving frame into contact with each other whenpositioning said first moving frame and said second moving frame at saidrespective accommodation positions without causing said frontmost lensgroup and said rear lens group to come into contact with each otherregardless of said adjustment of said supporting position of said lenssupporting frame.
 13. The lens barrel according to claim 12, whereinsaid support frame movement mechanism comprises a biasing device; andwherein said support frame movement mechanism brings said lenssupporting frame and said second moving frame into contact with eachother, with a biasing force of said biasing device, when said firstmoving frame and said second moving frame are positioned at saidrespective accommodation positions.
 14. The lens barrel according toclaim 12, wherein said support frame movement mechanism comprises: afirst cam follower formed on said first moving frame; a second camfollower formed on said second moving frame; and a cam ring which isdriven to rotate about said optical axis, said cam ring including a camgroove in which said first cam follower and said second cam follower areengaged; wherein said cam groove comprises: a frontmost lens groupmoving section for moving said first moving frame to saidready-to-photograph position; a rear lens group moving section formoving said second lens frame to said ready-to-photograph position; afrontmost lens group accommodation section for allowing said frontmostlens group to move to said accommodation position which is locatedbehind a position of said frontmost lens group in said optical axisdirection when said first cam follower is positioned in said frontmostlens group moving section; and a rear lens group accommodation sectionfor allowing said rear lens group to move to said accommodation positionwhich is located behind a position of said rear lens group in saidoptical axis direction when said second cam follower is positioned insaid rear lens group moving section; wherein said frontmost lens groupaccommodation section defines a clearance between said frontmost lensgroup accommodation section and said first cam follower so that saidfirst cam follower is movable in said optical axis direction in saidfrontmost lens group accommodation section, whereby said frontmost lensgroup and said rear lens group are not in contact with each other in astate where said lens supporting frame and said second moving frame arein contact with each other when said first moving frame and said secondmoving frame are located at said respective accommodation positions; andwherein said clearance includes at least a predetermined widthcorresponding to a maximum variation amount by said adjustment of saidsupporting position of said lens supporting frame.
 15. The lens barrelaccording to claim 12, wherein said support frame movement mechanismcomprises: a first cam follower formed on said first moving frame; asecond cam follower formed on said second moving frame; and a cam ringwhich is driven to rotate about said optical axis, said cam ringincluding a cam groove in which said first cam follower and said secondcam follower are engaged; wherein a width of said cam groove in saidoptical axis direction at a position corresponding to said accommodationposition, when said first moving frame is positioned at saidaccommodation position, is formed so that a clearance between said camgroove and said first cam follower is greater than an adjustment rangeof a position of said lens supporting frame relative to said firstmoving frame in said optical axis direction.
 16. The lens barrelaccording to claim 12, wherein said biasing device comprises at leastone helical compression spring.
 17. A lens barrel comprising: at leastone lens group which moves in an optical axis direction; a ring memberwhich is provided around said lens group, said ring member having aphotographing aperture at a front end thereof; and at least one barrierblade positioned at said front end of said ring member, said barrierblade being driven to open and close said photographing aperture;wherein a frontmost surface of said lens group is formed as a convexsurface; wherein said barrier blade includes a concave surface which isformed on a rear surface thereof so that a shape of said concave surfacecorresponds to a shape of a corresponding portion of said frontmostsurface; and wherein said barrier blade is driven to open and close saidphotographing aperture in a plane perpendicular to said optical axis ata position where collision between said barrier blade and said convexfront surface of said lens group is avoided due to the presence of saidconcave surface.
 18. The lens barrel according to claim 17, wherein saidlens group comprises a front lens group and a rear lens group, saidextendable lens barrel further comprising: a front lens support memberwhich supports said front lens group and is guided in said optical axisdirection without rotating about said optical axis; a rear lens supportmember which supports said rear lens group and is guided in said opticalaxis direction without rotating about said optical axis; and a supportframe movement mechanism for moving said front lens support member andsaid rear lens support member between respective ready-to-photographpositions and respective accommodation positions located behind saidrespective ready-to-photograph positions in said optical axis direction,respectively; wherein said support frame movement mechanism brings saidfront lens support member and said rear lens support member into contactwith each other at said respective accommodation positions withoutcausing said front lens group and said second lens group to come intocontact with each other.
 19. The lens barrel according to claim 18,wherein said support frame movement mechanism comprises a biasingdevice, and wherein said support frame movement mechanism brings saidfront lens support member and said rear lens support member into contactwith each other, with a biasing force of said biasing device, at saidrespective accommodation positions.
 20. The lens barrel according toclaim 18, wherein said front lens group comprises a frontmost lens groupof said lens group; wherein said front lens support member includes alens supporting frame to which said frontmost lens group is supported,and a first moving frame to which said lens supporting frame issupported via male and female screw-threaded portions meshing with eachother, one and the other of said male and female screw-threaded portionsbeing formed on said lens supporting frame and said first moving frame,respectively; wherein a supporting position of said lens supportingframe, relative to said first moving frame in said optical axisdirection, can be adjusted via said male and female screw-threadedportions during assembly; and wherein said support frame movementmechanism brings said lens supporting frame and said rear lens supportmember into contact with each other when positioning said front lenssupport member and said rear lens support member at said respectiveaccommodation positions without causing said frontmost lens group andsaid rear lens group to come into contact with each other regardless ofsaid adjustment of said supporting position of said lens supportingframe.
 21. The lens barrel according to claim 17, wherein each said lensgroup constitutes a lens element of a zoom lens optical system forvarying a focal length.
 22. The lens barrel according to claim 17,wherein said barrier blade comprises a pair of barrier blades; andwherein said concave surface comprises a pair of semi-circular concavefaces which are formed on said pair of barrier blades, respectively,said pair of semicircular concave faces together forming a circularconcave face, said circular concave face corresponding to the shape of acentral portion of said convex frontmost surface in a state where saidpair of barrier blades are closed.
 23. A lens barrel comprising: frontand rear lens groups guided in a direction of an optical axis withoutrotating about said optical axis; a first support frame which supportssaid front lens group, said first support frame including a first camfollower; a second support frame which supports said rear lens group,said second support frame including a second cam follower; and a camring which is driven to rotate about said optical axis, said cam ringincluding a first groove portion and a second groove portion in whichsaid first cam follower and said second cam follower are engaged,respectively; wherein said first groove portion includes a firstoperating section for moving said front lens group to a position whereina photographing operation is performed; and a first accommodationsection for moving said front lens group to a first accommodationposition which is located behind a position of said front lens group insaid optical axis direction when said first cam follower is positionedin said first operating section; wherein said second groove portionincludes a second operating section for moving said rear lens group toperform said photographing operation; and a second accommodation sectionfor moving said rear lens group to a second accommodation position whichis located behind a position of said rear lens group in said opticalaxis direction when said second cam follower is positioned in saidsecond photographing section; and wherein at least one of said firstaccommodation section and said second accommodation section is formed toallow corresponding at least one of said first cam follower and saidsecond cam follower to move in said optical axis direction incorresponding said at least one of said first accommodation section andsaid second accommodation section.
 24. The lens barrel according toclaim 23, wherein said first accommodation section and said secondaccommodation section are formed so that said front lens group and saidrear lens group are released from constraints of said firstaccommodation section and said second accommodation section at saidfirst accommodation position and said second accommodation position,respectively.
 25. The lens barrel according to claim 23, wherein saidcam groove is formed as a continuous groove including said first grooveportion and said second groove portion.
 26. The lens barrel according toclaim 25, wherein said first groove portion, said second groove portion,said first accommodation section and said second accommodation sectionare arranged in that order from one end of said cam groove, so that saidfirst cam follower passes through said second groove portion when movingbetween said first accommodation section and said first groove portion.27. The lens barrel according to claim 26, wherein said second operatingsection of said second cam groove is formed adjacent to said firstoperating section of said first cam groove portion, and wherein saidfirst accommodation section of said first cam groove portion is formedadjacent to said second operating section, and said second accommodationsection of said second cam groove is formed adjacent to said firstaccommodation section.
 28. A lens barrel comprising: a plurality of lensgroups guided in an optical axis direction without rotating about saidoptical axis; a plurality of support frames which support said pluralityof lens groups, respectively; a plurality of cam followers formed onsaid plurality of support frames, respectively; and a cam ring which isdriven to rotate about said optical axis, said cam ring including aplurality of cam grooves in which said plurality of cam followers areengaged, respectively; wherein each of said plurality of cam groovescomprises: a operating section for moving corresponding one of saidplurality of lens groups to perform a photographing operation; and anaccommodation section for moving said corresponding one lens group to anaccommodation position which is located behind a position of saidcorresponding one lens group in said optical axis direction whencorresponding one of said plurality of cam followers is engaged in saidoperating section; wherein at least one of said accommodation sectionsis formed to allow said corresponding one cam follower to move in saidoptical axis direction in said accommodation section.